Geohydrology, Geochemistry, and Ground-Water 

Simulation-Optimization of the Central and West 

Coast Basins, Los Angeles County, California

By Eric G. Reichard, Michael Land, Steven M. Crawford, Tyler Johnson, Rhett R. 

Everett, Trayle V. Kulshan, Daniel J. Ponti, Keith J. Halford, Theodore A. Johnson1, 

Katherine S. Paybins, and Tracy Nishikawa

Sacramento, California

2003

Water-Resources Investigations Report 03-4065

U.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

WATER REPLENISHMENT DISTRICT OF 

SOUTHERN CALIFORNIA 5025-32

1 Water Replenishment District of Southern California
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

For additional information write to:

District Chief

U.S. Geological Survey

Placer Hall—Suite2012

6000 J Street

Sacramento, CA 95819-6129

http://ca.water.usgs.gov

Copies of this report can be purchased from:

U.S. Geological Survey

Information Services

Building 810

Box 25286, Federal Center

Denver, CO 80225-0286
Contents iii

CONTENTS

Abstract ................................................................................................................................................................ 1

Introduction .......................................................................................................................................................... 2

Background ................................................................................................................................................. 2

Purpose and Scope ...................................................................................................................................... 4

Description of Study Area........................................................................................................................... 4

Acknowledgments....................................................................................................................................... 4

Data Compilation and New Data Collection........................................................................................................ 5

Geologic Framework............................................................................................................................................ 5

Hydrogeologic Framework .................................................................................................................................. 10

Recent Aquifer System ............................................................................................................................... 17

Lakewood Aquifer System.......................................................................................................................... 17

Upper San Pedro Aquifer System ............................................................................................................... 18

Lower San Pedro Aquifer System............................................................................................................... 19

Pico Unit...................................................................................................................................................... 19

Analysis of Hydraulic Conductivities ......................................................................................................... 19

Regional Ground-Water Flow System ................................................................................................................. 19

Sources and Movement of Water................................................................................................................ 19

Ground-Water Development....................................................................................................................... 20

Geochemical Analysis.......................................................................................................................................... 24

Introduction................................................................................................................................................. 24

Water-Quality Network...................................................................................................................... 24

Construction and Well Selection .............................................................................................. 24

Data Collection and Purpose..................................................................................................... 24

Definition of Hydrologic Regions and Aquifer Systems................................................................... 27

Ground-Water Quality ................................................................................................................................ 27

Dissolved Solids................................................................................................................................. 27

General Chemical Character .............................................................................................................. 33

Central Basin............................................................................................................................. 33

West Coast Basin ...................................................................................................................... 37

Dissolved Chloride............................................................................................................................. 37

Dissolved Oxygen.............................................................................................................................. 40

Dissolved Sulfate ............................................................................................................................... 40

Dissolved Manganese ........................................................................................................................ 46

Dissolved Iron.................................................................................................................................... 46

Isotopic Composition of Ground Water...................................................................................................... 46

Deuterium and Oxygen-18................................................................................................................. 46

Central Basin............................................................................................................................. 47

West Coast Basin ...................................................................................................................... 53

Tritium ............................................................................................................................................... 54

Central Basin............................................................................................................................. 55

West Coast Basin ...................................................................................................................... 60

Carbon-14........................................................................................................................................... 60

Central Basin............................................................................................................................. 64

West Coast Basin ...................................................................................................................... 64

Integrated Geochemical Analysis of the Regional Ground-Water Flow System ....................................... 67

Development of a Ground-Water Simulation Model........................................................................................... 72
iv Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Boundary Conditions .................................................................................................................................. 72

Model-Layer Elevations.............................................................................................................................. 77

Hydraulic Properties.................................................................................................................................... 82

Areal Recharge............................................................................................................................................ 82

Pumpage, Spreading, and Injection............................................................................................................. 97

Model Calibration ....................................................................................................................................... 97

Model-Parameter Sensitivity..............................................................................................................110

Analysis of Regional Ground-Water Budget with Ground-Water Simulation Model................................115

Model Sensitivity to Orange County Boundary Condition.........................................................................120

Model Limitations.......................................................................................................................................120

Applications of the Ground-Water Simulation Model.........................................................................................126

Particle Tracking Analyses .........................................................................................................................126

Simulation of Future Water-Management Scenarios..................................................................................130

Simulation-Optimization Analysis.......................................................................................................................147

Summary ..............................................................................................................................................................154

References Cited ..................................................................................................................................................156

Appendix I. Geographic Information System ......................................................................................................161

Appendix II. Well identification, Model Layer, and Aquifer-Systems information for 

U.S. Geological Survey Multiple-well Monitoring Sites, Los Angeles, California......................................162

Appendix III. Correlation between Specific Conductance and Dissolved-Solids Concentration........................166

Appendix IV. Parameters used to generate model layer elevation surfaces ........................................................167

Appendix V: Estimation of mountain front recharge for 1970–71 ......................................................................168

Appendix VI. Hydrographs of simulated and measured water levels, 1971–2000..............................................172
Figures v

FIGURES

Figure 1. Map showing surface geology of the study area, Los Angeles County, California........................... 3

Figure 2. Maps showing location of U.S. Geological Survey wells (A) and geohydrologic-section 

lines, wells with geophysical logs, and geologic structures (B) in the study area, 

Los Angeles County, California ........................................................................................................ 6

Figure 3. Chart showing geologic formations, aquifers, aquifer systems, and model layers in the 

Central and West Coast Basins, Los Angeles County, California..................................................... 9

Figure 4. Graphs showing geohydrologic sections A–A’’, B–‘B’, C–C’’, D–D’, and E–E’, 

in the study area, Los Angeles Country, California........................................................................... 11

Figure 5. Graph showing historical pumpage, injection, and spreading of water in the 

Central and West Coast Basins, Los Angeles County, California..................................................... 21

Figure 6. Map showing ground-water production in the study area in water year 2000, 

Los Angeles County, California ........................................................................................................ 22

Figure 7. Long-term hydrographs of water levels at selected wells in study area, 

Los Angeles County, California ........................................................................................................ 23

Figure 8. Map showing location of ground-water sampling sites and geochemical flow path 

cross sections in the study area, Los Angeles County, California..................................................... 25

Figure 9. Diagram showing components of typical USGS multiple-well monitoring site ............................... 26

Figure 10. Map and graphs showing distribution of dissolved-solids concentrations from sampled 

ground water and boxplot of concentrations in ground water from the Upper and Lower 

aquifer systems, in the Central and West Coast Basins, Los Angeles County, California................ 30

Figure 11. Graphs showing general chemical character of ground water sampled in the Central and 

West Coast Basins with grouping by total dissolved solids concentration, grouping by 

aquifer systems, and labelling of selected wells, Los Angeles County, California........................... 34

Figure 12. Map and graph showing dissolved-chloride concentration in ground water sampled in the 

study area, Los Angeles County, California ...................................................................................... 38

Figure 13. Map and graph showing dissolved-oxygen concentrations in ground water sampled in the 

study area, Los Angeles County, California ...................................................................................... 42

Figure 14. Map and graph showing dissolved sulfate concentrations in ground water sampled in the 

study area, Los Angeles County, California ...................................................................................... 44

Figure 15. Map and graph showing delta-deuterium values in ground water sampled in the 

study area, Los Angeles County, California ...................................................................................... 48

Figure 16. Graphs showing delta deuterium as a function of delta oxygen-18 in ground water sampled in 

the study area, in the Central Basin, in the West Coast Basin, Los Angeles County, California...... 50

Figure 17. Graph showing estimated tritium activities in precipitation, Los Angeles County, 

California (from Michel, 1989) ......................................................................................................... 56

Figure 18. Map and graphs showing tritium concentration in ground water sampled in the study area, 

Los Angeles County, California ........................................................................................................ 58

Figure 19. Map and graphs showing carbon-14 activities in sampled ground water in the study area, 

Los Angeles County, California ........................................................................................................ 62

Figure 20. Graphs showing dissolved-solids concentration, measurable tritium activity, and carbon-14 

activity in ground water from wells sampled along geohydrologic sections A’–A’’ and C’–B’, 

Los Angeles County, California ........................................................................................................ 68

Figure 21. Graph showing delta deuterium as a function of delta oxygen-18, grouped by tritium 

concentration in ground water sampled in the study area, Los Angeles County, California............. 71

Figure 22. Maps showing model grid and boundary conditions for the ground-water simulation model for 

layer 1, Recent aquifer system; layer 2, Lakewood aquifer system; and layers 3 and 4, 

Upper San Pedro and Lower San Pedro aquifer systems, Los Angeles County, California.............. 73
vi Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Figure 23. Map showing wells used for water-level calibration and head-dependant boundary 

conditions for ground-water simulation model, Los Angeles County, California............................. 76

Figure 24. Maps showing elevation of base of layers 1-4 of the ground-water simulation model: 

Recent aquifer system, Lakewood aquifer system, Upper San Pedro aquifer system, and 

Lower San Pedro aquifer system, Los Angeles County, California .................................................. 78

Figure 25. Maps showing hydraulic conductivities for layers 1–4 of the ground-water simulation model: 

Recent aquifer system, Lakewood aquifer system, Upper San Pedro aquifer system, and 

Lower San Pedro aquifer system, Los Angeles County, California .................................................. 83

Figure 26. Maps showing vertical conductances for the ground-water simulation model: between 

layers 1 and 2, Recent and Lakewood aquifer systems; between layers 2 and 3, Lakewood and 

Upper San Pedro aquifer systems; and between layers 3 and 4, Upper San Pedro and 

Lower San Pedro aquifer systems, Los Angeles County, California................................................. 87

Figure 27. Maps showing specific yield for layer 1 and storage coefficients for layers 2–4 of the 

ground-water simulation model: Recent aquifer system, Lakewood aquifer system, 

Upper San Pedro aquifer system, and Lower San Pedro aquifer system, 

Los Angeles County, California ........................................................................................................ 90

Figure 28. Map showing injection, spreading, and mountain-front recharge cells for the ground-water 

simulation model, Los Angeles County, California .......................................................................... 95

Figure 29. Map showing pumping cells for years 1971–2000 in ground-water simulation model, 

Los Angeles County, California ........................................................................................................ 98

Figure 30. Maps showing model-simulated and average measured water levels, 1971, for layers 1–4 

of the ground-water simulation model: Layer 1, Recent aquifer system; Layer 2, Lakewood 

aquifer system; Layer 3, Upper San Pedro aquifer system; and Layer 4, Lower San Pedro 

aquifer system, Los Angeles County, California............................................................................... 99

Figure 31. Maps showing model-simulated and average measured water levels, 2000, for layers 1–4 of 

the ground-water simulation model: Layer 1, Recent aquifer system; Layer 2, Lakewood 

aquifer system; Layer 3, Upper San Pedro aquifer system; and Layer 4, Lower San Pedro 

aquifer system, Los Angeles County, California...............................................................................103

Figure 32. Graphs showing simulated water levels as a function of measured water levels at calibration 

wells, model layers 1–4, Los Angeles County, California ................................................................109

Figure 33. Graphs showing sensitivity graphs for selected model parameters ...................................................113

Figure 34. Maps showing average model-simulated inter-zone flows for layers 1–4 for 1971–2000 and 

1996–2000, Los Angeles County, California ....................................................................................118

Figure 35. Graphs showing annual model-simulated flows between zones and from basins outside 

model area, 1971–2000, Los Angeles County, California.................................................................121

Figure 36. Maps showing model-simulated and measured water levels, 2000, with specified flow 

boundary at Orange County for layers 1–4 of the ground-water simulation model: Layer 1, 

Recent aquifer system; Layer 2, Lakewood aquifer system; Layer 3, Upper San Pedro 

aquifer system; and Layer 4, Lower San Pedro aquifer system, Los Angeles County, California....122

Figure 37. Map showing model-simulated backward tracking of advective flow paths of water particles 

from U.S. Geological Survey Downey-1 monitoring site in 1998 to their time of entry into the 

simulation model, Los Angeles County, California ..........................................................................128

Figure 38. Map showing model-simulated forward tracking of advective flow paths of water particles 

from spreading grounds, 1967–2000, Los Angeles County, California ............................................129

Figure 39. Maps showing model-simulated advective flow paths of water particles from coastline, 

Layer 3, 1971–2000 and from injection wells, 1971–2000, Los Angeles County, California ..........131

Figure 40. Map and graphs showing model-simulated drawdowns, layer 3 and selected model-simulated 

hydrographs for future scenario 1, 2001–25, Los Angeles County, California.................................137

Figure 41. Map and graphs showing model-simulated drawdowns, layer 3 and selected model-simulated 

hydrographs for future scenario 2, 2001–25, Los Angeles County, California.................................139
Figures vii

Figure 42. Maps showing average model-simulated inter-zone flows for layers 1–4 for future 

scenario 1, 2001–25, Los Angeles County, California ......................................................................141

Figure 43. Maps showing average model-simulated inter-zone flows for layers 1–4 for future 

scenario 2, 2001–25, Los Angeles County, California ......................................................................142

Figure 44. Map and graphs showing model-simulated drawdowns, layer 3 and selected model-simulated 

hydrographs for future scenario 1 with constant flow at the Orange County boundary, 

2001–25 .............................................................................................................................................143

Figure 45. Map and graphs showing model-simulated drawdowns, layer 3 and selected model-simulated 

hydrographs for future scenario 2 with constant flow at the Orange County boundary, 

2001–25 .............................................................................................................................................145

Figure 46. Map showing in-lieu and injection cells for the ground-water simulation model-optimization 

analysis, Los Angeles County, California .........................................................................................148

Figure 47. Graphs showing sensitivity of optimization results (injection rates, in lieu rates and total cost) 

to average head constraint, Los Angeles County, California.............................................................154

Figure 48. Graph showing sensitivity of optimization reslts to relative cost of injection and in-lieu water, 

Los Angeles County, California ........................................................................................................154
viii Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

TABLES

Table 1. Composition of selected waters in the study area, Los Angeles County, California......................... 28

Table 2. Carbon-14 and apparent-age for selected wells sampled, Los Angeles County, California.............. 65

Table 3. Processes and reactions controlling water quality along geohydrologic sections A’–A” 

and C’–B’, Los Angeles County, California...................................................................................... 70

Table 4. Hydraulic characteristic values used in the ground-water simulation model .................................... 94

Table 5. Annual precipitation at LACDPW Downey Station 107D and recharge and pumpage used in 

ground-water simulation model ......................................................................................................... 96

Table 6. Sensitivity of model parameters ........................................................................................................ 111

Table 7. Average 30-year water budget for historic ground-water simulation, 1971–2000 ........................... 116

Table 8. Average 5-year water budget for historic ground-water simulation, 1996–2000.............................. 117

Table 9. Inputs used for future model scenarios (2001–25) ........................................................................... 133

Table 10. Average water budget for future scenario 1, 2001–2025................................................................... 135

Table 11. Average water budget for future scenario 2, 2001–2025................................................................... 136

Table 12. Summary of optimization results....................................................................................................... 151

Table 13. Results from iterative solution for optimization run 1 (base case) .................................................... 152

Table 14. Average reduced cost for in lieu cells, for optimization run 1 (base case) ....................................... 153
Conversion Factors, Vertical Datum, and Abbreviations ix

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

CONVERSION FACTORS 

Temperature in degrees Celsius (oC) may be converted to degrees Fahrenheit (oF) as follows:

oF=1.8 oC+32.

VERTICAL DATUM

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD 

of 1929)—a geodetic datum derived from a general adjustment of the first-order level nets of both the 

United States and Canada, formerly called Sea Level Datum of 1929. 

Altitude, as used in this report, refers to distance above or below sea level.

ABBREVIATIONS

oC degrees Celcius

δ delta

GIS Geographic Information System

mg/L milligrams per liter

NIU Newport Inglewood Uplift

pCi/L picocuries per liter

per mil parts per thousand, as used with delta (δ) notation

pmc percent modern carbon

PVC polyvinyl chloride

RMSE root mean square error

SMCL Secondary Maximum Contaminant Level

SS sum-of-square error

TDS total dissolved solids

TU tritium unit

Multiply By To obtain

acre 0.004047 square kilometer

foot (ft) 0.3048 meters

acre foot (acre-ft) 1,233. cubic meter 

cubic foot (ft3) 0.02832 cubic meter

gallon (gal) 3.785 liter

inch (in.) 0.3048 meters

mile (mi) 1.609 kilometers

square mile (mi2) 2.590 square kilometer
x Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

μg/L micrograms per liter

μS/cm microsiemens per centimeter at 25oC

UTM Universal Transverse Mercator

VSMOW Vienna Standard Mean Ocean Water

yr year

Organizations

LACDPW Los Angeles County Department of Public Works

USGS U.S. Geological Survey

WRDSC Water Replenishment District of Southern California
Well-Numbering System xi

WELL-NUMBERING SYSTEM

Wells are identified and numbered according to their location in the rectangular system for the subdivision of 

public lands. Identification consists of the township number, north or south; the range number, east or west; and the 

section number. Each section is divided into sixteen 40-acre tracts lettered consecutively (except I and O), 

beginning with "A" in the northeast corner of the section and progressing in a sinusoidal manner to "R" in the 

southeast corner. Within the 40-acre tract, wells are sequentially numbered in the order they are inventoried. The 

final letter refers to the base line and meridian. In California, there are three base lines and meridians; Humboldt 

(H), Mount Diablo (M), and San Bernardino (S). All wells in the study area are referenced to the San Bernardino 

base line and meridian (S) Well numbers consist of 15 characters and follow the format 004S012W005H05S. In 

this report, well numbers are abbreviated and written 4S/12W-5H5. Wells in the same township and range are 

referred to only by their section designation, 5H5. The following diagram shows how the number for well 

4S/12W-5H5 is derived.

4S/12W-5H5

D C B A

E F G H

M L K J

N P Q R

6 5 4 3 2 1

7 8 9 10 11 12

18 17 16 15 14 13

19 20 21 22 23 24

30 29 28 26 25

31 32 33 34 35 36

27

R11W R10W

T3S

T2S

T1S

R12W

RANGE

TOWNSHIP

R14W R13W

T4S

T5S

Approximately

6 miles

Approximately

1 mile

Approximately

1/4 mile

R12W

Well-numbering diagram (Note: maps in this report use abbreviated well numbers such as "5H5")

SECTION 5

T4S

Abstract 1

Geohydrology, Geochemistry, and Ground-Water 

Simulation-Optimization of the Central and West Coast 

Basins, Los Angeles County, California

By Eric G. Reichard, Michael Land, Steven M. Crawford, Tyler Johnson, Rhett R. Everett, 

Trayle V. Kulshan, Daniel J. Ponti, Keith J. Halford, Theodore A. Johnson, Katherine S. 

Paybins, and Tracy Nishikawa

ABSTRACT

Historical ground-water development of the 

Central and West Coast Basins in Los Angeles 

County, California through the first half of the 

20th century caused large water-level declines and 

induced seawater intrusion. Because of this, the 

basins were adjudicated and numerous groundwater management activities were implemented, 

including increased water spreading, construction 

of injection barriers, increased delivery of 

imported water, and increased use of reclaimed 

water. In order to improve the scientific basis for 

these water management activities, an extensive 

data collection program was undertaken, 

geohydrological and geochemical analyses were 

conducted, and ground-water flow simulation and 

optimization models were developed.

In this project, extensive hydraulic, 

geologic, and chemical data were collected from 

new multiple-well monitoring sites. On the basis 

of these data and data compiled and collected from 

existing wells, the regional geohydrologic 

framework was characterized. For the purposes of 

modeling, the three-dimensional aquifer system 

was divided into four aquifer systems—the 

Recent, Lakewood, Upper San Pedro, and Lower 

San Pedro aquifer systems. Most pumpage in the 

two basins is from the Upper San Pedro aquifer 

system. 

Assessment of the three-dimensional 

geochemical data provides insight into the sources 

of recharge and the movement and age of ground 

water in the study area. Major-ion data indicate the 

chemical character of water containing less than 

500 mg/L dissolved solids generally grades from 

calcium-bicarbonate/sulfate to sodium 

bicarbonate. Sodium-chloride water, high in 

dissolved solids, is present in wells near the coast. 

Stable isotopes of oxygen and hydrogen provide 

information on sources of recharge to the basin, 

including imported water and water originating in 

the San Fernando Valley, San Gabriel Valley, and 

the coastal plain and surrounding hills. Tritium 

and carbon-14 data provide information on 

relative ground-water ages. Water with abundant 

tritium (greater than 8 tritium units) is found in 

and downgradient from the Montebello Forebay 

and near the seawater barrier projects, indicating 

recent recharge. Water with less than measurable 

tritium is present in, and downgradient from, the 

Los Angeles Forebay and in most wells in the 

West Coast Basin. Water from several deep wells 

was analyzed for carbon-14. Uncorrected 

estimates of age for these samples range from 600 

to more than 20,000 years before present. 

Chemical and isotopic data are combined to 

evaluate changes in chemical character along flow 

paths emanating from the Montebello and Los 

Angeles Forebays.
2 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

A four-layer ground-water flow model was 

developed to simulate steady-state ground-water 

conditions representative of those in 1971 and 

transient conditions for the period 1971–2000. 

Model results indicate increases in ground-water 

storage in all parts of the study area over the 

simulated thirty-year period. The model was used 

to develop a three-dimensional ground-water 

budget and to assess impacts of two alternative 

future (2001–25) ground-water development 

scenarios—one that assumes continued pumping 

at average current rates and a second that assumes 

increasing pumping from most wells in the Central 

Basin. The model simulates stable or slightly 

increasing water levels for the first scenario and 

declining water levels (25 to 50 ft in the Central 

Basin) in the second scenario. Model sensitivity to 

parameter values and to the assumed Orange 

County boundary condition was evaluated. 

Particle tracking was applied to simulate advective 

transport of water from the spreading ponds, the 

coastline, and the seawater injection barriers. 

Particle tracking results indicate that most flow 

within the Upper San Pedro aquifer system occurs 

within about 20 percent of the total aquifer system 

thickness and that virtually all water injected into 

the seawater barrier projects has flowed inland. 

The simulation model was linked with 

optimization to identify the least-cost strategies for 

improving hydraulic control of seawater intrusion 

in the West Coast Basin by means of increased 

injection and (or) in-lieu delivery of surface water. 

For the base-case optimization analysis, assuming 

constant ground-water demand, in-lieu delivery 

was determined to be most cost effective. Several 

sensitivity analyses were conducted with the 

optimization model. Raising the imposed average 

water-level constraint at the hydraulic-control 

locations resulted in non-linear increases in cost. 

Systematic varying of the relative costs of 

injection and in-lieu water yielded a trade-off 

curve between relative costs and injection/in-lieu 

amounts. Changing the assumed future scenario to 

one of increasing Central Basin pumpage caused a 

small (7-percent) increase in the computed costs of 

seawater intrusion control. 

INTRODUCTION

Background

Water use and water needs have been very 

closely tied to the development of greater Los Angeles, 

from its agricultural origins through its subsequent 

urbanization. As stated by Mendenhall (1905b) “...the 

story of the growth of this region becomes a story of 

the utilization and application of its available waters.” 

Since the first water wells were drilled about 150 years 

ago, ground water has been a significant component of 

water supply in the region. In the Central and West 

Coast Basins (fig. 1), which are the focus of this report, 

ground-water development through the first half of the 

20th century resulted in large water-level declines and 

associated problems such as seawater intrusion. This 

led to the adjudication of the basins in the early 1960s 

and the initiation of ground-water management 

activities including injection, spreading, pumping 

restrictions, and delivery of surface water to replace 

some pumping. Ground water currently supplies about 

one third of the water supply for the 4 million people 

who live in the Central and West Coast Basins. 

Sound management of the ground-water 

resources of the Central and West Coast Basins 

requires understanding of the geohydrology and 

geochemistry of the region. The first regional 

assessment of ground-water conditions in the Los 

Angeles coastal area was completed by Mendenhall 

(1905a,b,c). A series of reports by Poland and coworkers (Piper and Garrett, 1953; Poland and others, 

1956; Poland and others, 1959) provided a detailed 

description of the geology, geohydrology, and groundwater chemistry of the area. A series of reports by the 

California Department of Water Resources (1961, 

1962, 1966) presented an analysis of the regional 

geohydrology, including explicit delineation of 

aquifers. The Central and West Coast Basins are within 

the Los Angeles Geologic Basin. Overviews of the 

geology and tectonic history of the Los Angeles Basin 

were provided by Yerkes and others (1965) and Wright 

(1991). 
Introduction 3

Gabriel

Gabriel

River

San

Ballona Creek

San

Rio

Hondo

River

Los

Los

R

River

Angeles

Angeles

NewportInglewood

Uplift

West Coast

Basin Barrier

Project

Dominguez Gap

Barrier Project

Alamitos Gap

Barrier Project

Long Beach

Signal

Hill

Repetto Hills

Elysian

Hills

Merced Hills

Puente Hills

Dominguez

Hills

Palos Verdes Hills

San

Valley Gabriel

San Fernando Valley

Santa Monica Mountains

Los Angeles

Huntington

Beach

Seal Beach

Orange County

Los Angeles County

Los Angeles Basin ground-

 water simulation model

 boundary

Los Angeles – Orange 

County Boundary

Seawater barrier project Spreading grounds

0 10 MILES Geology from Tinsley and Fumal, 1985;

Hecker, and others, 1998;

California Department of Water Resources, 1961

Base map from U.S. Geological

Survey digital maps 1:24,000;

Bathymetric contours from 

U.S. Geological Survey 0 10 KILOMETERS

EXPLANATION

33°40'

50'

34°

34°10'

118°30' 20' 10' 118°00'

Pacific Ocean

Santa Monica Bay

San Pedro Bay

Central Basin

West Coast Basin

Hollywood Basin

Santa Monica

Basin

Montebello

Pressure

Area

Forebay

Los Angeles

Forebay

Whittier

Narrows

Alamitos

Gap

Los

Angeles

 Narrows

Holocene sediments

Pleistocene deposits

Tertiary deposits

Tertiary volcanic rocks

Mesozoic bedrock

Fault

Fold axis

Los Angeles

CALIFORNIA

San

Francisco

San Diego

Los Angeles

County

Study

area

Dominguez Gap

Figure 1. Surface geology of the study area, Los Angeles County, California.
4 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Although numerous studies have been conducted 

on specific ground-water issues in the Central and 

West Coast Basins, there has been no regional 

assessment of the regional geohydrology and 

geochemistry since the work of the California 

Department of Water Resources in the 1960s and no 

development of a three-dimensional computer 

simulation model of the multi-aquifer ground-water 

system. 

Purpose and Scope

The objectives of the work described in this 

report were to characterize the three-dimensional 

regional ground-water flow system and geochemistry 

in the Central and West Coast Basins and to develop 

and apply appropriate models for evaluating groundwater management issues in the Central and West 

Coast Basins in Los Angeles County, California. This 

work was conducted by the U.S. Geological Survey 

(USGS) during 1995–2002 in cooperation with the 

Water Replenishment District of Southern California 

(WRDSC). The report describes data compilation and 

new data collection, provides an overview of the 

geologic/hydrogeologic frameworks and the groundwater flow system, details the regional geochemistry, 

documents the development of a regional ground-water 

simulation model, and describes the use of the model 

and its linkage with optimization methods to evaluate 

alternative water-management strategies.

Description of Study Area

The study area, shown in figure 1, lies within the 

coastal part of the greater Los Angeles metropolitan 

area. The study area is bounded by the Santa Monica 

Mountains to the north; the Elysian, Repetto, Merced, 

and Puente Hills to the northeast; Orange County to the 

southeast; and the Pacific Ocean (Santa Monica Bay 

and San Pedro Bay) and the Palos Verdes Hills to the 

west and southwest. The study area incorporates the 

four coastal ground-water basins in Los Angeles 

County: the Central Basin, the West Coast Basin, the 

Hollywood Basin, and the Santa Monica Basin 

(California Department of Water Resources, 1961). 

The total onshore area covered by these four basins is 

about 480 mi2. All four basins are considered generally 

in this report; however, the focus is on the Central and 

West Coast Basins.

The study area is drained by three main rivers; 

the Los Angeles River, the San Gabriel River, and the 

Rio Hondo (fig. 1). The Los Angeles River, which 

drains the San Fernando Valley to the north, enters the 

study area through the Los Angeles Narrows. The San 

Gabriel River and Rio Hondo, which drain the San 

Gabriel Valley to the northeast, enter the study area 

through the Whittier Narrows. The areas downstream 

from the Los Angeles Narrows and the Whittier 

Narrows are known as the Los Angeles Forebay and 

the Montebello Forebay, respectively. As described 

later, these forebay areas were delineated by the 

California Department of Water Resources (1961) as 

areas where surface water could freely percolate into 

the ground-water system. The non-forebay part of the 

Central Basin, where such percolation is more 

restricted, is referred to as the Pressure Area. 

Acknowledgments

The Water Replenishment District of Southern 

California cooperatively funded this study. The Los 

Angeles County Department of Public Works and the 

City of Santa Monica provided essential data. The 

individuals who assisted in the data collection and the 

many entities that provided access for sampling and 

drilling are listed in the companion report of Land and 

others (2002). Paul Barlow, Robert Michel, 

Louis Murray Jr., Roy Schroeder, James Baker, 

Anthony Buono, Phil Contreras, Devin Galloway, 

Mary Gibson, Julia Huff, Rick Iwatsubo, 

Clark Londquist, Alice McCracken, Laurel Rogers, 

Larry Schneider, and Jerry Woodcox all contributed to 

the review and processing of this report. 

Anthony Brown, Joe Hevesi, Joe Montrella, Tony 

Kirk, Bennett Chong, and Mario Garcia provided 

assistance and support for the project. 
Data Compilation and New Data Collection 5

DATA COMPILATION AND NEW DATA 

COLLECTION

A major component of this study was developing 

a Geographic Information System (GIS) for the study 

area. The GIS, which is a spatially relational database, 

serves as a tool for combining data and geographic 

features from a variety of sources. It also provides a 

mechanism for analyzing combinations of data, 

visualizing the data, and interfacing the data with other 

applications, including a ground-water model. The GIS 

can store features and attributes of the ground-water 

system, analyze data between spatial layers, and 

display data in the form of maps and graphics. Details 

of the GIS are in Appendix I.

Development of the GIS enabled the compilation 

and coordinated analysis of the existing data for the 

study area. However, despite the abundance of existing 

data, it was necessary to collect new data to 

significantly improve the understanding of the regional 

ground-water flow system. Most existing data 

(collected prior to this investigation) for the study area 

are collected from production wells with large screened 

intervals. The two major data-collection tasks in this 

study have been the drilling and logging of multiplewell monitoring sites and conducting water-quality 

sampling and analysis. 

This report incorporates data collected at 24 new 

multiple-well monitoring sites (fig. 2A). The spatial 

distribution of the sites encompasses the Montebello 

Forebay, the Whittier area, the Los Angeles Forebay, 

the Pressure Area of the Central Basin, and the West 

Coast Basin. Each multiple-well site consists of four to 

six polyvinyl chloride (PVC) monitoring wells 

installed at different depths in the same drill hole. 

Perforated intervals of the different wells are isolated 

from one another by low-permeability bentonite grout. 

Considerable data have been collected from each 

monitoring site. The cuttings were logged as the well 

was drilled. Two to four cores were collected during 

the drilling of each site and were analyzed for 

hydraulic properties. Geophysical and temperature logs 

were conducted at each well. Water levels were 

measured regularly and water-quality samples were 

collected and analyzed. 

The data collected from these monitoring sites 

provide information on the vertical variability of 

hydraulic properties, water levels, and water quality at 

each site. This depth-dependent information is needed 

to improve the characterization of the threedimensional ground-water system. A compilation of 

data collected from the monitoring sites is provided by 

Land and others (2002). A summary of construction 

information for these sites is in Appendix II

GEOLOGIC FRAMEWORK

The current understanding of the structural and 

tectonic history of the Los Angeles Basin has been 

described by Wright (1991); he summarizes and builds 

on a considerable body of previous work, including the 

seminal work of Yerkes and others (1965). The Los 

Angeles Basin is at the northern end of the Peninsular 

Ranges geomorphic province. Structurally, the 

Peninsular Ranges province is characterized by fault 

zones that trend northwest to west-northwest. The Los 

Angeles Basin is of considerable geologic interest as an 

area of major oil-production and active seismicity.

The study area of this report lies within the 

central and southwestern structural blocks of the Los 

Angeles Basin. The Central and Hollywood groundwater basins are within the central block, and the West 

Coast and Santa Monica ground-water basins (fig. 2) 

are within the southwestern block. The NewportInglewood Uplift (NIU) is a northwest-trending zone 

that separates the central and southwestern blocks 

(fig.1). The NIU extends from Beverly Hills southeast 

to Newport Beach in southern Orange County. The 

fault zone can be projected at least 45 mi southward 

offshore (Wright, 1991). The NIU is a series of en 

echelon anticlinal folds and discontinuous faults. It is 

characterized by wrench-style deformation, which is 

inferred to be predominantly right-lateral strike slip 

(Harding, 1973; Yeats, 1973). Total displacement 

along the NIU is estimated to be less than 2 mi (Hill, 

1971). 
6 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Gabriel

Gabriel

Ballona Creek

River

San

San

Rio

Hondo

River

Los

R Angeles

Los

Los

R

River

Angeles

Angeles

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Pressure

Area

Repetto Hills Repetto Hills

Elysian Elysian

Hills

Elysia

Hil

n

ls

Merced Hills Merced Hills

Puente Hills Puente Hills

Merced Hills

Puente Hills

San

Valley

Gabriel

Santa Monica Mountains

Orange County

Palos Verdes

Hills

Los Angeles

County

Signal

Hill

Dominguez

Hills

Santa Monica Bay

San Pedro Bay

Fault

Fold axis

Unconsolidated deposits

EXPLANATION

Consolidated deposits

Geology not mapped for

 this study

Los Angeles Basin 

 ground-water 

 simulation model 

 boundary.

Seawater barrier project

USGS Multiple well 

 monitoring site 

Spreading grounds

West Coast

Basin Barrier

Project

Dominguez Gap

Barrier Project

Alamitos Gap

Barrier Project

A

Whittier

Narrows

Los Angeles

Narrows

Base map from U.S. Geological

Survey digital maps 1:24,000 Geology from Tinsley and Fumal, 1985;

Hecker, and others, 1998;

California Department of Water Resources, 1961

Long

Beach

Los Angeles

Seal Beach

Huntington

Beach

Beverly

Hills

Newport - Ingle wood- Uplift

Palos Verdes

Fault Zone

Wilmington Syncline

Gardena

Syncline

Paramount

Syncline

Fault

Pico

Wilmington Anticline

Railroad- grade Fault

Dominguez Channel

Rosecrans

Anticline

Rio

Hondo

Fault Whittier

Fault

Norwalk Fault

Los Alamitos Fault

Reservoir Hill Fault

Portrero

Fault

Charnock

Fault

Santa Monica

Fault

Portrero Canyon Fault

Overland

Fault Inglewood

Fault

Seal Beach

Fault

Cherry

Hill Fault

Northeast

Flank Fault

Dominguez

Anticline

Santa Fe

Springs

Avalon- Anticline

Compton

Fault

Baldwin

Hills

Dominguez Gap

5H5-10

1N3-8

8J1-4

28A3-7 26A2-7

32F1-5

32F1-5

9H9-12

9J1-6 9D1-5

26D9-14 25G3-8

26E2-6

5P9-14

25G1-6

2K4-8

7J1-6

22C1-5

6B4-8

17F1-5

13J5-8

28M3-7

26N3-6

17G3-8

18C4-7

0 10 MILES

0 10 KILOMETERS

33°

40'

50'

34°

00'

118°30' 20' 10' 118°00'

R16W R15W R14W R13W R12W R11W R10W

T5S T4S T3S T2S T1S

Figure 2. Location of U.S. Geological Survey wells (A) and geohydrologic-section lines, wells with geophysical logs, and geologic structures (B) in the 

study area, Los Angeles County, California.
Geologic Framework 7

Newport -

InglewoodUplift

Gabriel

Gabriel

River

San

San

Rio

Hondo

River

Los

Los

R

River

Angeles Angeles Los

R

Angeles

Angeles

Ballona

Creek

A'

B

D

D'

E

C

C''

C'

B'

A''

E'

A

5H5-10

1N3-8

8J1-4

28A3-7 26A2-7

9H9-12

9J1-6 9D1-5

26D9-14

26E2-6

25G1-6

2K4-8

7J1-6

22C1-5

6B4-8

17F1-5

13J5-8

28M3-7

26N3-6

17G3-8

18C4-7

32F1-5

32F1-5

23D3-7

5P9-14

0 10 MILES

0 10 KILOMETERS

33°

40'

50'

34°

00'

118°30' 20' 10' 118°00'

Well data from California 

 Department of Water 

 Resources (1961)

R16W R15W R14W R13W R12W R11W R10W

T5S T4S T3S T2S T1S

Pacific

Ocean

Los Angeles

Forebay

Montebello

Forebay

Whittier

Area

Pressure

Area

Signa

H

l

ill

Huntington

Beach

Santa Monica Bay

San Pedro Bay

Whittier

Narrows

Los Angeles

Narrows

West Coast

Basin Barrier

Project

Dominguez Gap

Barrier Project

Alamitos Gap

Barrier Project

Fault Fold axis

Unconsolidated deposits

Consolidated deposits

Geology not mapped 

 for this study

Los Angeles Basin ground-

 water simulation model

 boundary

Seawater barrier project

Spreading grounds

USGS multiple well monitoring 

 site with geophysical logs

Non USGS wells with 

 geophysical logs

EXPLANATION

B

Base map from U.S. Geological

Survey digital maps 1:24,000

Pressure

Area

Geology from Tinsley and Fumal, 1985;

Hecker, and others, 1998;

California Department of Water Resources, 1961

Beverly

Hills

25G3-8

Repetto Hills Repetto Hills Repetto Hills

Elysian Elysian

Hills

Elysia

Hil

n

ls

Merced Hills Merced Hills

Puente Hills Puente Hills

Merced Hills

Puente Hills

Santa Monica Mountains

Palos Verdes

Hills

Dominguez

Hills

Baldwin

Hills

Santa Monica

Basin

West Coast

Basin

Central

Basin

Hollywood

Basin

Gabriel

Orange County

Los Angeles

County

Long

Beach

Los Angeles

Seal Beach

San

Valley

Figure 2.—Continued.
8 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

The faults and folds of the NIU include Beverly 

Hills, Baldwin Hills, Inglewood Fault, Portrero Fault, 

Rosecrans Anticline, Avalon-Compton Fault, 

Dominguez Anticline, Cherry Hill Fault, Railroad 

Grade Fault, Northeast Flank Fault, Reservoir Hill 

Fault, and Seal Beach Fault (fig. 2). Wright (1991) 

excludes Beverly Hills from the NIU, considering them 

to be a part of the Santa Monica Fault system. Yerkes 

and others (1965) stated that oil field data indicate 

middle Miocene displacement along the NIU and noted 

that the “arching and erosion of marine upper 

Pleistocene and of younger nonmarine strata in the hills 

along the zone, and numerous seismic shocks,...attest 

to continuing activity.” The NIU has been considered 

to approximately coincide with the boundary between 

western basement Catalina Schist and eastern basement 

granitic rocks (California Department of Water 

Resources, 1961; Yerkes and others, 1965). Wright 

(1991) stated that this distinction between the eastern 

basement and western basement material is less clearly 

defined. 

Yerkes and others (1965) divided the geologic 

and structural evolution of the Los Angeles Basin into 

five phases: (1) predepositional phase, (2) prebasin 

phase of deposition, (3) basin inception phase, 

(4) principal phase of subsidence and deposition (upper 

Miocene to lower Pleistocene), and (5) basin disruption 

(upper Pleistocene to Holocene). Biddle (1991) stated 

that recent research has begun to address the 

underlying processes, but that the five phases of Yerkes 

and others (1965) have generally remained valid. Of 

main relevance to the geohydrology are phases 4 and 5. 

Subsequent research has incorporated new 

understanding of the effects of plate tectonics on the 

formation of the Los Angeles Basin. During Phase 4, 

much of the present form of the current Los Angeles 

Basin was established (Yerkes and others 1965). 

Wright (1991) described the multiple tectonic 

mechanisms at work during this period. 

Blake (1991) detailed the complexities of the 

nomenclature for Pliocene sediments in the subsurface 

of the Los Angles Basin. He described the Pico 

Formation in the Los Angeles Basin as upper Pliocene 

to upper Pleistocene deposits containing “lower middle 

bathyal to neritic deposits” (fig. 3). Poland and others 

(1956, 1959) defined the Pico formation in 

hydrostratigraphic terms; the lower and middle 

divisions consist of sandstone, siltstone, and claystone 

and the upper division of “semi-consolidated sand, silt, 

and clay of marine origin.” This hydrostratigraphic 

unit, which is referred to as the Pico unit throughout 

this report, does not necessarily correlate to the Pico 

formation as defined biostratigraphically in Blake 

(1991). 

Also deposited in the Palos Verdes Hills area 

during the early Pleistocene were the Lomita Marl, 

Timms Point Sand, and San Pedro Sand members of 

the San Pedro Formation. In this area, which contains 

the type section of the San Pedro Formation described 

by Woodring and others (1946), the San Pedro 

Formation unconformably overlies the lower Pliocene 

and Miocene deposits. In contrast, the San Pedro 

Formation conformably overlies Pliocene deposits on 

the south margins of the Puente Hills. Poland and 

others (1956, 1959) described the San Pedro Formation 

in the subsurface as including virtually all Pleistocene 

strata of predominantly marine origin that overlie the 

Pico hydrostratigraphic unit. Ponti (1989) stated that 

the subsurface San Pedro Formation is middle to upper 

part of the lower Pleistocene in age and appears to 

conformably overlie the Pico Formation in the 

southwest part of the Los Angeles Basin. Yerkes and 

others (1965) described the San Pedro Formation as 

consisting of marine silt, sand, and gravel deposited at 

moderate to shallow depths. Blake (1991) states that 

the San Pedro Formation represents a transition from 

inter-neritic deposits to nonmarine deposits. In this 

report, two hydrostratigraphic units are identified in the 

San Pedro Formation: a lower San Pedro unit that was 

deposited in deep water and includes local turbidite 

deposits and an upper San Pedro unit that apparently 

was deposited in shallower water and consists of 

packages of regressional sequences. 
Geologic Framework 9

Modified from California Department of

Water Resources, 1961; Ponti, 1989

HOLOCENE 1

2

3

4

UPPER

PLEISTOCENE

UPPER

PLIOCENE

LOWER

PLEISTOCENE

OLDER DUNE SAND

SAN

PEDRO

FORMATION

LAKEWOOD

FORMATION

(UNNAMED

UPPER

PLEISTOCENE,

Poland and

others 1956, 1959)

PICO

FORMATION

RECENT

AQUIFER

SYSTEM

LAKEWOOD

AQUIFER

SYSTEM

Lower

Aquifer

Systems

Lower

Aquifer

Systems

UPPER

SAN PEDRO

AQUIFER

SYSTEM

Upper

Aquifer

Systems

Pico

unit

LOWER

SAN PEDRO

AQUIFER

SYSTEM

GASPUR

HOLLYDALE

JEFFERSON

SILVERADO

SUNNYSIDE

LOWER

SAN PEDRO

LYNWOOD

(400 FOOT GRAVEL)

EXPOSITION

GARDENA

GAGE

(200 FOOT SAND)

ACTIVE DUNE SAND SEMIPERCHED

BALLONA

(California Dept.

of Water Resources, 1961)

AGE FORMATION AQUIFER AQUIFER

SYSTEMS

MODEL

LAYER

ARTESIA

Aquifer systems grouping for geochemical analysis

EXPLANATION

Figure 3. Geologic formations, aquifers, aquifer systems, and model layers in the Central and West Coast Basins, Los Angeles County, California.
10 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Yerkes and others (1965) described Phase 5 of 

basin development in the Los Angeles Basin as being 

characterized by tectonic uplift and erosion during the 

mid-Pleistocene, resubmergence and marine deposition 

during the late Pleistocene, and uplift and alluvial 

deposition from the late Pleistocene to the Holocene. 

Davis and others (1989) described this as a period of 

compressional shortening. Ponti (1989) used 

aminostratigraphic techniques to determine that, in the 

southern part of the West Coast Basin, most of the 

apparent disruption during this period was the result of 

eustatic sea-level changes rather than tectonic activity. 

During the late Pleistocene, shallow-water marine 

sediments [referred to as unnamed upper Pleistocene 

deposits by Poland and others (1956, 1959)] including 

the Palos Verdes Sand of Woodring and others (1946), 

as well as nonmarine fluvial, alluvial, and eolian 

sediments were deposited. These late Pleistocene 

deposits are referred to collectively by the California 

Department of Water Resources (1961) as the 

Lakewood Formation. Yerkes and others (1965) 

characterized the upper Pleistocene deposits as 

consisting of marine terrace deposits, nonmarine 

terrace cover in the southwestern block (West Coast 

Basin), and nonmarine fluvial and lagoonal deposits in 

the central block (Central Basin). An angular 

unconformity exists between the middle part of the 

upper Pleistocene Lakewood formation and the 

underlying San Pedro Formation in some locations. 

Late Pleistocene and Holocene sediments were 

deposited in canyons incised into the Pleistocene 

deposits during sea-level low stands (Yerkes and 

others, 1965; Ponti, 1989). Gaps (including the 

Dominguez and Alamitos Gaps) were cut into the 

rising hills along the NIU, and channels were cut into 

the emerged sea bottom. When sea level rose again, 

these entrenched channels and gaps were filled with 

sequences of fluvial, lagoonal, and estuarine deposits. 

The California Department of Water Resources (1961) 

stated that the incising of the channels occurred during 

sea level low stand during the most recent glacial 

period (60,000 yr before present to 15,000 yr before 

present), and that the channels were then filled with 

Holocene deposits as sea levels rose. The basal part of 

these channel deposits is coarse grained and very 

permeable. Away from the channels in alluvial-fan and 

flood-plain depositional environments, thin layers of 

sand and silty sand were deposited (Yerkes and others, 

1965). Ponti (1989) suggested that several stages of 

cutting and filling occurred during both Pleistocene 

and Holocene time and that the basal zone contains 

restricted marine deposits as well as fluvial deposits. 

Although all the deposits above the Lakewood 

Formation will be referred to as recent deposits in the 

remainder of this report, it is important to keep in mind 

that some of these deposits are likely of Pleistocene 

age.

HYDROGEOLOGIC FRAMEWORK

The first characterizations of the aquifers in the 

Los Angeles coastal basins were completed by Poland 

and co-workers (Poland and others, 1956, 1959). The 

California Department of Water Resources (1961) built 

on the work of Poland and further analyzed the groundwater flow system. Identified aquifers are shown in the 

stratigraphic column in figure 3. Cross sections 

developed by the California Department of Water 

Resources (1961) were, for the most part, based on 

drillers’ logs. 

One goal of the current study was to develop 

new sections utilizing geophysical logs along with 

ancillary information, including geochemical data. 

About 150 geophysical logs were compiled and 

digitized (fig. 2B). Five cross sections, A–A’’, B–B’, C–

C’’, D–D’, and 

E–E’ (figs. 2B and 4) were developed for this study. 

The sections were chosen to include new USGS 

monitoring sites and to cover as much of the Central 

and West Coast Basins as possible. Only electrical 

resistivity logs are shown in figure 4; however, 

spontaneous potential (SP), natural gamma ray, caliper, 

and geologic logs of drill cuttings also were evaluated 

where available. For this study, aquifers were grouped 

into four aquifer systems: the Recent, Lakewood, 

Upper San Pedro, and Lower San Pedro aquifer 

systems (fig. 3). The Pico unit also is shown and is 

defined as a non-transmissive zone that underlies the 

lower San Pedro aquifer system. Factors considered in 

defining the aquifer systems include unconformities, 

lithology, depositional characteristics, geochemistry, 

and vertical water-level differences. Considerable 

emphasis was placed on the characteristics of the 

geophysical logs.
Hydrogeologic Framework 11

28D1 18C4-7

Holocene

Pleistocene

Pliocene

Aquifer system

USGS multiple-well monitoring site

Non USGS well 

Fault – Dashed where acts

as partial barrier to groundwater flow, queried where

uncertain

Geologic contact – Dashed

where approximately located,

queried where uncertain

Screened

interval

Abbreviated well number

Electric log

Geologic age

Lakewood

Recent

Upper San Pedro

Lower San Pedro

Pico unit

Increasing resistivity

Well casing

Increasing resistivity

Electric log

Well casing

Abbreviated well number

? ?

EXPLANATION

Figure 4

Figure 4. Geohydrologic sections A–A’’, B–‘B’, C–C’’, D–D’, and E–E’, in 

the study area, Los Angeles Country, California (lines of sections are shown 

in figure 2B). 
12 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California Figure 4.—Continued.

?

?

?

?

?

?

?

?

?

?

A''

A

Sea

400

400

level

FEET

800

1,200

1,600

2,000

2,400

?

? ?

?

5G5

8C

27R2

28D1

17N

19C

26F5

28N4

28A3-7

5H5-10

9J1-6

26D9-14

18C4-7

3J1

32F1-5

31N1

7D

7H

00 5 KILOMETERS

5 MILES

Paramount

Syncline

Pico Fault

Wilmington Anticline

Section

C-C"

Section

D-D'

Section

E-E'

Wilmington Syncline

Palos Verdes

Faults

NewportInglewood

Uplift

Los Angeles River

Dominguez Channel

Vertical scale greatly exaggerated Datum is sea level

A'
Hydrogeologic Framework 13

400

Sea

level

400

800

1,200

1,600

2,000

2,400

B B' FEET 34F 11E4 15E2 32R15 22C1-5 23R33N 13J5-8 8J1-4 5E

Datum is sea level Vertical scale greatly exaggerated

?

0

0 5 KILOMETERS

5 MILES

Neport Inglewood Uplift

Section

E-E'

Section

D-D'

Sections

C-C", D-D'

Figure 4.—Continued.
14 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Figure 4.—Continued.

?

?

?

400

Sea

level

400

800

1,200

1,600

2,000

2,400

C C' C'' 1L 35M5 2E 8J1-4 9H9-12 28A3-7 27P2 33X28Q 21X Dominguez Channel Newport- Inglewood Uplift Dominguez Channel Section A-A" Section B-B', D-D'

Datum is sea level Vertical scale greatly exaggerated

0

0 5 KILOMETERS

5 MILES

FEET
Hydrogeologic Framework 15

?

?

?

?

? ?

? ?

D' D

Sea

400

level

400

800

1,2001,6002,0002,400

27D

28G5

26E2-6

26J

28D1

20F8

12P

15F

10A4

13J5-8

17G3-8

8J1-4

Rosecrans

Anticline

Gardena Symcline

Chamock fault

Paramount

Syncline

00 5 KILOMETERS

5 MILES

Section

B-B", C-C"

Section

A'-A"

Section

B-B' FEET

Vertical scale greatly exaggerated Datum is sea level

Figure 4.—Continued.
16 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

?

?

?

? ?

0

0 5 KILOMETERS

5 MILES

 level Vertical scale greatly exaggerated

Figure 4.—Continued.
Hydrogeologic Framework 17

Recent Aquifer System

 The geohydrologic units that compose the 

Holocene (Recent) age deposits of the Recent aquifer 

system include the semiperched aquifer, the Bellflower 

aquiclude, the Gaspur aquifer, and the Ballona aquifer 

(California Department of Water Resources, 1961). 

Although these geohydrologic units are referred to in 

this report as consisting of Holocene-age deposits, 

some of these units consist of deposits of Pleistocene 

age. The semiperched aquifer is a relatively thin layer 

of coarse sand and gravel near the land surface; it 

consists of alluvial sediments and, in parts of the West 

Coast Basin, marine deposits that may include the late 

Pleistocene Palos Verdes Sand. Because of low yields 

and poor water quality, little water is pumped from the 

semiperched aquifer. Except in parts of the Montebello 

and Los Angeles Forebay areas, this semiperched zone 

is separated from the underlying aquifers by a zone of 

lower permeability materials referred to as the 

Bellflower aquiclude. The Bellflower aquiclude is very 

heterogeneous and includes all of the fine grained 

sediments that extend from the ground surface or from 

the base of the semiperched aquifer, down to the 

underlying aquifer (California Department of Water 

Resources, 1961). 

The coarse, basal zone of the Recent aquifer 

system is called the Gaspur aquifer. The California 

Department of Water Resources (1961) defined the 

extent of the Gaspur aquifer to be limited to two lobes 

in the Montebello and Los Angeles Forebays merging 

near the city of Downey and extending along the 

current Los Angeles River channel through the 

Dominguez Gap to the ocean. In the forebay areas, the 

Gaspur aquifer is nearly all sand and gravel. Hydraulic 

conductivities have been reported as high as 800 ft/d 

(California Department of Water Resources, 1961). 

Although the Ballona aquifer, which extends 

along the western part of the Ballona Creek channel in 

the Santa Monica Basin, also consists of Holocene 

(Recent) deposits, it is not explicitly included in the 

Recent aquifer system in the model developed for this 

study. The Ballona aquifer is the stratigraphic 

equivalent of the Gaspur aquifer and may have been 

deposited by the Los Angeles River system (including, 

perhaps, the downstream reaches of the Rio Hondo and 

San Gabriel River) when it flowed out into Santa 

Monica Bay. The yield of the Ballona aquifer is quite 

variable and the Ballona aquifer is not a major source 

of water supply.

Delineating the Recent aquifer system can be 

difficult because parts of its deposits are unsaturated 

and geophysical information is not dependable. 

However, the basal Gaspur aquifer is indicated by a 

high-resistivity zone in some of the logs. There also 

tends to be an SP shift and an increase in the natural 

gamma emission below the Gaspur aquifer. The 

Gaspur aquifer is typically 40 to 50 ft of coarse pebbly 

sand. Depth to the base of the Gaspur ranges from close 

to land surface to 175 ft below land surface. Geologic 

logs indicate oxidized conditions at shallow depths that 

may indicate Pleistocene deposition. The Holocene 

deposits were likely laid down rapidly and underwent 

little oxidation. The uppermost Pleistocene deposits, in 

contrast, likely were deposited more slowly and 

subjected to oxidation. The use of a surficial geology 

map developed by John Tinsley (U.S. Geological 

Survey, written commun., 1997) helped determine, 

when other sources of evidence were not conclusive, 

whether or not Holocene deposits were present.

Lakewood Aquifer System

The main aquifers of the Lakewood aquifer 

system are the Exposition, Artesia, Gardena, and Gage 

aquifers (fig. 3). Generally, the Lakewood aquifer 

system is a heterogeneous unit dominated by sandy 

silts and silty sands interbedded with sands that 

become coarser and thicker near the base of the aquifer 

system. Gamma logs from many wells show the 

alternating lithologies in the upper part of the 

Lakewood aquifer system; the lower coarse-grained 

units typically are indicated by decreases in gamma 

emissions. Because deposition of the Lakewood 

Formation was controlled by sea-level fluctuations, 

pre-existing topography, and, to a lesser extent, 

subsidence or uplift, the Lakewood aquifers have 

varying thicknesses and degrees of sorting. The entire 

Lakewood aquifer system ranges in thickness from 150 

to 400 ft. 
18 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Sediments within the Exposition and Artesia 

aquifers in the upper part of the Lakewood Formation 

(fig. 3) are considered to have been deposited 

contemporaneously. The Exposition aquifer is 

associated with the Los Angeles River and the Artesia 

aquifer with the San Gabriel River (California 

Department of Water Resources, 1961). The 

Exposition aquifer is very heterogeneous and 

characterized by discontinuous sand and gravel zones 

separated by silt and clay lenses. The Artesia aquifer 

consists of coarse gravel, coarse to fine sand, and 

interbedded silts and clays. The age of parts of both 

aquifers may be similar to deposits that form the 

Gaspur aquifer (California Department of Water 

Resources, 1961). The Exposition and Artesia aquifers 

commonly are poorly defined or absent. 

The Gardena and Gage aquifers are at the base of 

the Lakewood Formation (fig. 3). The Gage aquifer 

was referred to by Poland and co-workers(1956, 1959) 

as the 200-foot sand—although, as noted by California 

Department of Water Resources (1961) and confirmed 

during this study, the depth to the base of the 

Lakewood aquifer system can be considerably deeper 

than 200 ft in the Central Basin (fig. 4). The Gardena 

aquifer consists of coarse deposits of probable fluvial 

origin that are inset into the dominantly shallow-water 

deposits that compose the Gage aquifer. The Gage 

aquifer consists of sand and gravel with lenses of sandy 

silt, silty clay, and clay. In this study, the Gage and 

Gardena aquifers were viewed as a single but complex 

aquifer system that is a source for water supply in some 

parts of the study area. 

Upper San Pedro Aquifer System

The Upper San Pedro aquifer system 

incorporates the Hollydale, Jefferson, Lynwood, and 

Silverado aquifers (fig. 3). An angular unconformity 

exists between the Lakewood Formation and the 

underlying San Pedro Formation. The boundary 

between the Lakewood aquifer system and the Upper 

San Pedro aquifer system is identified on most 

geophysical logs by a shift in the SP log and a change 

in the character of both the gamma and resistivity logs. 

Large resistivity spikes, with accompanying SP shifts 

and decreases in natural gamma emission, coincide 

with the coarse-grained productive aquifers within the 

Upper San Pedro system. The Upper San Pedro aquifer 

system thins toward the margins of the forebays and at 

structural highs such as those along the NIU. This 

thinning is presumed to result, in part, from midPleistocene emergence (as sea level declined) and 

subsequent erosion. In the Los Angeles Forebay area, 

the Upper San Pedro aquifer system appears to be finer 

grained overall than elsewhere in the basin. 

The Hollydale and Jefferson aquifers are the 

uppermost aquifers within the Upper San Pedro aquifer 

system. The California Department of Water Resources 

(1961) defines the areal extent of both aquifers to be 

limited to the Central Basin. Neither aquifer is 

considered an important source of water supply. The 

Hollydale aquifer is presumed to contain fluvial 

deposits in the northern part of the basin—in the Los 

Angeles and Montebello Forebays—and shallow 

marine deposits in the southern part. The underlying 

Jefferson aquifer was defined strictly on the basis of 

drillers’ logs and is considered to be generally fine 

grained (California Department of Water Resources, 

1961). Individual units correlative with the Hollydale 

and Jefferson aquifers are definable only locally. 

The Lynwood aquifer is an important source of 

water. It is believed to consist of continental deposits in 

the forebay area and shallow marine deposits to the 

south and west. The Lynwood aquifer is seen on many 

resistivity logs as upward-coarsening sequences as 

indicated by upward-increasing resistivities.

The Silverado aquifer is in the lower part of the 

Upper San Pedro aquifer system (fig. 3) and produces 

the most water in the study area. In its type area, in 

Long Beach, the Silverado aquifer has been correlated 

to the marine San Pedro Sand by Poland and others 

(1956, 1959). In some areas the Silverado aquifer is 

associated with sediment deposited by the ancestral 

Rio Hondo and San Gabriel River systems (California 

Department of Water Resources, 1961). Overall, the 

aquifer system appears to be of mixed origin, with 

nonmarine deposits consisting of sand and gravel that 

are interbedded with silt and clay, and marine deposits 

characterized by blue-gray sand, gravel, silt, and clay, 

along with shells and wood fragments. The Silverado 

aquifer merges with overlying aquifers in the forebay 

areas. It also merges with both overlying and 

underlying aquifers near Santa Monica Bay (California 

Department of Water Resources, 1961). In many wells, 

the resistivity log for the Silverado aquifer indicates a 

fining-upward package.
Regional Ground-Water Flow System 19

Lower San Pedro Aquifer System

The Lower San Pedro aquifer system includes 

the Sunnyside aquifer (also referred to as the Lower 

San Pedro aquifer). The upper part of this system tends 

to be characterized by alternating fine-grained and 

coarse-grained zones. The fine-grained zones tend to 

pinch out or disappear near the forebay margins, such 

as at USGS Pico Rivera-1 (2S/11W-18C4–7) and 

1S/13W-34F (fig. 4A,B). The coarsest part of the 

aquifer system generally is at the base and is as much 

as 100 ft thick. The Lower San Pedro aquifer system 

becomes very shallow and merges with the Upper San 

Pedro aquifer system in both the Los Angeles and 

Montebello Forebay areas. Most of the geophysical 

logs compiled in this study do not reach the base of the 

Lower San Pedro aquifer system. The total thickness of 

the Lower San Pedro aquifer system is as at least 600 ft 

in the center of the Central Basin. The typical 

resistivity-log signature of the Lower San Pedro 

aquifer system can be seen at the USGS Lakewood-1 

(4S/12W-5H5–10) monitoring site at depths greater 

than 790 ft (fig. 4A).

Pico Unit

Underlying these four aquifer systems is the Pico 

hydrostratigraphic unit. On resistivity logs, the unit is 

characterized by a flat, low-resistivity signature. 

Resistivity within the Pico unit in some zones 

(generally 10 ft thick or less) is higher than that in 

some of the overlying units. This high resistivity may 

reflect thin zones of higher consolidation and (or) 

better water quality.

Analysis of Hydraulic Conductivities

Laboratory estimates of saturated vertical 

hydraulic conductivity were made from 48 cores taken 

at the USGS monitoring sites (Land and others, 2002, 

table 33). These values give some indication of the 

range of vertical hydraulic conductivities in the aquifer 

systems. Cores were generally taken in finer grained 

material; good recovery was not possible in the 

coarsest materials. Vertical hydraulic conductivity 

values ranged from less than 2.8 x 10-5 to 8 ft/d with a 

geometric mean of 2.7 x 10-2 ft/d. The vertical 

hydraulic conductivity estimates can be categorized by 

the lithologic description of the drill cuttings for that 

interval. The geometric mean vertical hydraulic 

conductivity of cores taken in materials described as 

predominantly clay, silt, and sand was 3.9 x 10-3 ft/d, 

1.0 x 10-2 ft/d, and 1.0 x 10-1 ft/d, respectively. 

Slug tests were conducted at 69 USGS wells 

(Land and others, 2002, table 32). The estimated 

hydraulic conductivities, computed for two assumed 

values of specific storage (1.0 x 10-4 and 

1.0 x 10-6 ft-1), ranged from 11 to 27 ft/d in the Recent 

aquifer system (2 wells), 1 to 140 ft/d in the Lakewood 

aquifer system (15 wells), 3 to 70 ft/d in the Upper San 

Pedro aquifer system (34 wells), 1.5 to 65 ft/d in the 

Lower San Pedro aquifer system (16 wells), and 0.1 to 

8 ft/d in the Pico unit (2 wells). An assumption in the 

slug-test analysis is that the imposed stress affects the 

entire perforated interval of the well. In general, the 

slug tests appear to underestimate hydraulic 

conductivities relative to those computed from multiwell aquifer tests (for example, Attachment 2, table C, 

California Department of Water Resources, 1961). 

Complete discussion of the procedures and analyses 

used for the slug tests is provided by Land and others 

(2002).

REGIONAL GROUND-WATER FLOW 

SYSTEM

Sources and Movement of Water

The ground-water system is recharged by direct 

precipitation, irrigation return, stream recharge, runoff 

from the surrounding uplands, artificial recharge of 

water through spreading grounds, injection of water in 

the seawater-barrier wells, and underflow from 

adjacent basins. Recharge from streams is limited 

because most of the streams are concrete lined. The 

Los Angeles River is lined throughout the study area 

except just upstream from where it enters San Pedro 

Bay. The San Gabriel River is lined except in the upper 

parts of the Montebello Forebay and near the Alamitos 

Gap, and the Rio Hondo is lined throughout the study 

area. The study area is hydraulically linked to three 

adjacent basins: the San Fernando Valley to the north, 

the San Gabriel Valley to the northeast, and the Orange 

County Basin to the southeast. 
20 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Under current conditions, most recharge occurs 

in the Montebello Forebay. This recharge includes 

artificial recharge in spreading ponds adjacent to the 

Rio Hondo and the San Gabriel Rivers and within the 

stream channels (fig. 1). Even before the artificialrecharge program began, the Montebello Forebay was 

a major recharge area because of the unconfined 

conditions and the presence of the San Gabriel River 

and Rio Hondo. No artificial recharge is conducted 

within the Los Angeles Forebay. The California 

Department of Water Resources (1961) stated that, 

because of its more highly urbanized conditions, 

natural recharge in the Los Angeles Forebay has been 

less than that in the Montebello Forebay. 

Before significant ground-water development 

began, ground water moved from the forebay areas 

(and from the Santa Monica Mountains on the 

northwest) south and west toward the Santa Monica 

and San Pedro Bays. Water moved laterally outward 

and vertically downward to underlying confined 

aquifers. The water eventually discharged either in 

wetlands or offshore. 

The NIU is a major structural feature that acts as 

a partial barrier to ground-water flow between the 

Central and West Coast Basins. Other faults (fig. 2) in 

the study area also appear to have hydraulic effects. 

Poland and others (1959) stated that faults in the Los 

Angeles area affect ground-water flow because of 

displacement of units and cementation within fault 

zones. The degree to which different faults affect flow 

in different aquifers is uncertain. The ground-water 

simulation model developed as part of this study has 

been used to test hypotheses regarding the permeability 

effects of faults. The California Department of Water 

Resources (1961) discussed the hydraulic effects of 

faults (and other structures) within the NIU, including 

the Rosecrans Anticline and the Inglewood, Portrero, 

Avalon-Compton, Cherry Hill, and Northeast (NE) 

Flank, Reservoir Hill, and Seal Beach Faults (fig. 2). 

Bawden and others (2001) used interferometric 

synthetic aperture radar (InSAR) to correlate seasonal 

land deformation with ground-water pumpage. Their 

results clearly showed a discontinuity in land 

deformation across the southern part of the NIU. 

Because the NIU affects interflow between the Central 

and West Coast Basins, considerable effort has been 

directed at quantifying the ground-water flow rates 

across it. (Montgomery Watson, 1993). Further 

discussion of flow across the NIU is provided later as 

part of the water-budget analysis of the ground-water 

modeling section of this report. 

In addition to the NIU, Poland and others (1959) 

noted water-level discontinuities associated with the 

Charnock and Overland Faults in the West Coast Basin 

(fig. 2). In the Central Basin, the Pico, Rio Hondo, and 

Los Alamitos Faults may restrict flow in the aquifers in 

Pleistocene sediments (California Department of Water 

Resources, 1961). In the Santa Monica Basin, the Santa 

Monica and Portrero Canyon Faults potentially restrict 

ground-water flow in Pleistocene formations (Wright, 

1991; Pratt and others, 1998). As can be seen in 

figure 2, there are numerous other faults in the study 

area that may affect ground-water flow. In addition, 

there likely are unmapped faults that are affecting 

ground-water movement. 

Ground-Water Development

The first water wells were drilled in the mid1800s, and by the early 1900s there were more than 

4,000 wells in the study area (Mendenhall, 1905a,b,c). 

Poland and others (1959) reported the presence in 1895 

of a flowing well 2 mi north of Signal Hill that had 

water levels 80 ft above land surface. Mendenhall 

(1905a,b,c) reported many flowing wells in the area. At 

that time, approximately 30 percent of the area was 

under flowing artesian conditions. 

 Historical quantities of pumping, injection, and 

spreading in the Central and West Coast Basins are 

shown in figure 5. Note in figure 5 that pumpage for 

1935–57 is from the California Department of Water 

Resources (1962), whereas that for 1961–2000 was 

reported to the Water Masters and published in 2000 by 

Water Replenishment District of Southern California 

(WRDSC).
Regional Ground-Water Flow System 21

400,000

RECHARGE/EXTRACTION, IN ACRE-FEET PER YEAR

No data

200,000

1920 1940 1960

YEAR

1980 2000

0

Pumpage

Injection

Spreading

From 1900 to 1930, pumpage increased 

considerably owing to increasing urban demand, lack 

of surface-water supplies, and development of the deep 

well turbine (Poland and others, 1959). By the 1920s, 

water levels were below sea level throughout much of 

the West Coast Basin. The entire ground-water flow 

system had changed dramatically; ground water no 

longer discharged into wetlands or offshore. Instead, 

seawater began moving inland in aquifers from both 

Santa Monica Bay and San Pedro Bay. By the 1940s 

elevated chloride owing to seawater intrusion was 

noted in all coastal areas (Poland and others, 1959, 

Pl. 16). The continuing trend through the 1950s was 

one of increasing pumpage (fig. 5) coupled with a shift 

from agricultural to urban water use. The increase in 

ground-water pumpage led to further declines in water 

levels. In many ground-water basins, large groundwater-level declines are accompanied by land 

subsidence. Poland and others (1959, p. 145) stated that 

ground-water withdrawals likely caused some 

subsidence in the West Coast Basin, but that it was not 

possible to quantitatively distinguish between 

subsidence strictly caused by ground-water pumping 

and subsidence caused by tectonic effects and to 

hydraulic connection to oil-producing areas. More 

recently, the InSAR work of Bawden and others (2001) 

showed significant seasonal land-surface oscillation in 

parts of the Central Basin that correlates with seasonal 

pumping patterns. They also saw evidence of possible 

longer term land-surface changes between 1993 and 

1999. 

Paralleling the increasing ground-water pumping 

were two important surface-water developments: 

importation of water via pipelines and use of surface 

water for artificial recharge. Importation of water 

began in 1913 when water from Owens Valley was 

first delivered to the area via the Los Angeles 

Aqueduct. In 1948, Colorado River water was first 

delivered to the area via the Colorado Aqueduct. In the 

late 1930s, spreading of local runoff in ponds in the 

Montebello Forebay began. In the early 1950s, 

imported water began to be used for this spreading. 

Also in the 1950s, well injection of imported water at 

what is now the West Coast Basin Barrier Project 

(fig. 2) began on an experimental basis; the principal 

goal of this injection was to create a hydraulic barrier 

to seawater intrusion.

Figure 5. Historical pumpage, injection, and spreading of water in the Central and West Coast Basins, Los Angeles 

County, California.
22 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Gabriel

San

Rio Hondo

Ballona Creek

River

Los

River

Angeles

Gabriel

River

San

Rio

Hondo

Los

River

Angeles

Montebello

Forebay

Los Angeles

Forebay

Long Beach

Carson

Signal Hill

Hills

Dominguez

Palos Verdes Hills

Los Angeles

Lakewood

Wilmington

Lomita

Seal Beach

Gardena

Inglewood

Compton

Downey

Orange County

Los Angeles County

South

Gate

Commerce

La Mirada

Santa Fe Springs

Pico

Rivera

Hawthorne

0 5 MILES

0 5 KILOMETERS

EXPLANATION

San Gabriel Valley

San Gabriel Valley

Pacific Ocean

Santa Monica

Bay

San Pedro Bay

18°30' 25' 20' 05' 15' 10' 118°00'

50'

33°

45'

55'

34°

05'

34°

00'

Repetto Hills

Elysian

Hills

Merced Hills

Puente Hills

Santa Monica Mountains

Unconsolidated deposits

Consolidated deposits

Los Angeles coastal basin –

Los Angeles Basin ground-

 water simulation model

 boundary

Spreading grounds

Other basins

Forebay

Seawater barrier project

Ground-water production

for 2000 – In acre feet per year

Less than 500 

501 - 2,000 

Greater than 2,000

West 

Coast

Basin

Barrier

Project

Dominguez Gap

Barrier Project

Alamitos Gap

Barrier Project

West Coast Basin

Central Basin

Hollywood Basin

Santa Monica

Basin

R15W R14W R16W R14W R13W R12W R11W

T5S T5S T5S T5S T5S T5S

Figure 6. Ground-water production in the study area in water year 2000, Los Angeles County, California.
Regional Ground-Water Flow System 23

Figure 7. Long-term hydrographs of water levels at selected wells in study area, Los Angeles County, California.

24M3,8

12K1

21H5

22P1

10A1

28H9

21B2

22L1

Los Angeles Basin

Los Angeles Basin

Model boundary

120

80

40

-40

-80

-120

-140

-80

-120

-40

40

80

120

160

120

80

40

-40

-80

1930 1940 1950 1960 1970 1980 1990 2000 1930 1940 1950 1960 1970 1980 1990 2000

-120

-80

-40

40

80

120

-120

-80

-40

40

80

120

-120

-80

-40

40

80

120

Los Angeles Forebay

Central Basin Pressure Area

Montebello Forebay

West Coast Basin West Coast Basin

Central Basin Pressure Area

2S/13W-10A1

LACDPW No. 2778

2S/12W-24M3

LACDPW No. 1601P

2S/12W-24M8

3S/14W-22L1

LACDPW No. 760C

3S/14W-21B2

LACDPW No. 1349/1349A

4S/12W-28H9

LACDPW No. 460K

LACDPW No. 1601T

4S/13W-12K1

LACDPW No. 906D

Well No.4S/13W-22P1

LACDPW No. 869

Well No.4S/13W-21H5

LACDPW No. 868H

WATER LEVEL IN FEET ABOVE SEA LEVEL

Sea

Level

Sea

Level

Sea

Level

Sea

Level

Sea

Level

Sea

Level

YEAR YEAR
24 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

The continuing depletion of ground-water 

storage eventually led to the adjudication of both the 

Central and West Coast Basins in the early 1960s. The 

WRDSC was formed in 1959 to protect and manage 

ground water in the two basins. The dramatic changes 

that occurred after the basins were adjudicated are 

illustrated in figure 5. In particular, there were large 

decreases in pumpage and large increases in injection 

and spreading rates. The pumpage decreases reflect the 

increasing direct use of imported water. The injection 

and spreading increases reflect the construction of new 

facilities (the Alamitos Gap Barrier Project in 1965 and 

the Dominguez Gap Barrier Project in 1971) and the 

increasing use of imported and reclaimed water. 

Reclaimed water began to be used for spreading in the 

1960s and for injection at the West Coast Basin Barrier 

Project in the 1990s. An additional source of imported 

water, the State Water Project, became available in the 

1970s.

The distribution of pumpage for water year 2000 

is shown in figure 6. It can be seen from figure 6 that 

there is a greater density of active production wells in 

the Central Basin relative to the West Coast Basin and 

that there are several local areas of concentrated 

pumpage throughout the study area.

Long-term hydrographs for key wells monitored 

by Los Angeles County are shown in figure 7. The 

hydrographs clearly show the long-term declines 

though the mid-1950s, the differing patterns of postadjudication recovery in different parts of the study 

area, and the change in annual and seasonal trends in 

parts of the Central Basin Pressure Area since the mid1990s. 

GEOCHEMICAL ANALYSIS 

Introduction

Water-Quality Network

Ground-water samples were collected from 

170 wells at 78 ground-water sites from August 1995 

to May 2001 (fig. 8). Additional chemical data from 

the California Department of Health Services Title-22 

monitoring program (California Department of Health 

Services, 1998), the Los Angeles County Department 

of Public Works Hydrologic Report (Los Angeles 

County Department of Public Works, 1998), and the 

Water Replenishment District Regional Groundwater 

Monitoring Report (Water Replenishment District of 

Southern California, 2000) were compiled.

Construction and Well Selection

The ground-water quality network includes 

24 multiple-well monitoring sites (Appendix II), 

20 existing observation wells, and 38 existing 

production wells. Nearly all samples were collected 

from the Central and West Coast ground-water basins; 

a few samples were from adjacent ground-water basins. 

The multiple-well monitoring sites consist of four to 

six wells installed at various depths within a single 

borehole and vertically sealed using bentonite grout 

(fig. 9).

Existing observation and production wells were 

incorporated into the monitoring network to help meet 

additional water-quality data-collection needs. 

Observation wells sampled as part of this study are 

screened over relatively short intervals, typically 10 to 

40 ft, to provide information from a single waterbearing unit. These 20 wells are constructed of 2- or 

4-inch-diameter PVC or galvanized steel. Existing 

production wells sampled as part of this study were 

designed for municipal water supply. Production wells 

were selected for sampling on the basis of location and 

limited perforated range (commonly less than 100 ft). 

Unlike observation wells, some of these wells have a 

screened interval that is open to several water-bearing 

units; consequently, water from these wells is a mixture 

of water from those units. 

Data Collection and Purpose

Water-quality samples were collected using a 

portable submersible pump or at a spigot near the 

production well head. Water-level depth, specific 

conductance, pH, temperature, dissolved oxygen, and 

alkalinity were recorded during the collection 

process.To assess general water-quality conditions and 

study the chemical character of the ground water, 

samples were analyzed for major ions, nutrients, and 

trace elements. To study the source and movement of 

ground-water recharge through the basin, samples were 

analyzed for the stable isotopes of deuterium (2H) and 

oxygen-18 (18O). To estimate the residence time of 

water in the ground, samples were analyzed for the 

radioisotopes tritium (3H) and carbon-14 (14C). Datacollection procedures, well identification and 

construction, and other information from the 

monitoring network utilized in this report are presented 

by Land and others (2002).
Geochemical Analysis 25

Geology not mapped

 for this study

Whittier

Area

Gabriel

San

Rio Hondo

River

Los

River

Angeles

Gabriel

River San

Rio

Hondo

Los

River

Angeles

Ballona Creek

R15W R14W R13W R12W R11W

A'

C"

C'

C

B'

A''

A' A"

2N1,2

31C3 31H1

24L1

9D1

15N1 18J5

1E1

20N3

31H2

1N3

1D2

24M8

1E2

27E2

28L1

25D1

2N3,4

13F4

35D4

10L3

2H4

35Q5

23H3,17

28H1

25E1

15A11

6K1,4

10Q2

17D2

26C1

6D2

11R4

5J1 7G1

21M1

12J1

32R13

14F1

16H1

21R3

11B3

10H1

3J1

11E1

33A7

28J6

34F1

22L1

3K2

30K2

25C1 19E2

11R4

5H5-10 1N3-8

8J1-4

28A3-7

26A2-7

32F1-5

9H9-12

9J1-6

9D1-5

26D9-14

25G3-8

26E2-6

5P9-14

25G1-6

2K4-8

7J1-6

22C1-5

6B4-8

17F1-5

13J5-8

28M3-7

26N3-6

17G3-8

18C4-7

USGS multiple-well monitoring site and number

Production well and number – Wells with perforations located in the:

Upper aquifer systems Lower aquifer systems

Other well and number – Wells with perforations located in the:

Upper aquifer systems Lower aquifer systems

0 5 MILES

0 5 KILOMETERS

EXPLANATION

San Gabriel Valley

Pacific Ocean

Santa

Monica

Bay

San Pedro Bay

18°25' 20' 05' 15' 10' 118°00'

50'

33°45'

55'

34°00'

34°05'

West 

Coast Basin 

Barrier Project

Dominguez

Gap Barrier

Project Alamitos Gap

Barrier Project

32F1-5

25E1

24M8 15N1

10L3

Repetto Hills

Elysia

H

n

ills

Merced Hills

Puente Hills

Santa Monica Mountains

Unconsolidated deposits

Consolidated deposits

Spreading grounds

Line of section (see figure 20)

Seawater barrier project

Dominguez

Hills

Signal Hill

Palos Verdes Hills

Orange

County

Los Angeles

County

Model subareas

West Coast Basin

Central Basin

Hollywood Basin

Santa

Monica

Basin

Montebello Forebay

Los Angeles

Forebay

T1S T2S T3S T4S T5S

Whittier

Narrows

Los Angeles

Narrows

Model boundary

Dominguez Gap

Figure 8. Location of ground-water sampling sites and geochemical flow path cross sections in the study area, Los Angeles County, California.
26 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Figure 9. Components of typical USGS multiple-well monitoring site.

100

0

200

300

Total depth 897 feet

400

500

DEPTH, IN FEET BELOW LAND SURFACE

600

700

800

900

Drill method: hydraulic mud rotary

Horizontal scale greatly exaggerated.

Borehole

(bottom of hole

approximately

8 inches in diameter)

Well screen

(20 feet in height)

Well casing

(2 inches in diameter)

View from top of typical borehole 

Well vault as it appears on surface

Borehole

(top of hole 

approximately

12 inches in diameter)

Well

vault

Grout

Grout

Grout

Grout

Grout

Grout

Sand

Sand

Native

Soil

Sand

Sand

Sand

#3 #4

#5

#2

#1
Geochemical Analysis 27

Definition of Hydrologic Regions and Aquifer Systems

For the purpose of evaluating the regional 

ground-water quality and geochemical conditions, data 

collected from wells are divided into three groups 

following the model-layer hydrostratigraphy: the 

Upper aquifer systems, which include the Recent and 

Lakewood aquifer systems; the Lower aquifer systems, 

which include the Upper San Pedro and Lower San 

Pedro aquifer systems; and the Pico unit (fig. 3). 

Discussion of much of the geochemical data is 

grouped by subareas with emphasis on the USGS 

multiple-well monitoring sites. In the Central Basin, 

the subareas and the multiple-well monitoring sites 

associated with them, are the Montebello Forebay 

(Pico Rivera-1, Pico Rivera-2, and Rio Hondo-1), Los 

Angeles Forebay (Huntington Park-1 and Los 

Angeles-1), Pressure Area near the forebays 

(Willowbrook-1, South Gate-1, Commerce-1, and 

Downey-1), Pressure Area distal to the forebays 

(Inglewood-2, Lakewood-1, Cerritos-1, and Long 

Beach-1 and -2), and Whittier Area (Whittier-1 and 

Santa Fe Springs-1). In the West Coast Basin, the 

subareas and the multiple-well monitoring sites 

associated with them are the interior margin 

(Gardena-1 and Carson-1) and coastal margin 

(Hawthorne-1, Wilmington-1, and Wilmington-2).

Ground-Water Quality

In general, the quality of most water in the study 

area is suitable for industrial and public supply. 

Dissolved-solids concentrations are low throughout 

most of the aquifers, often less than 500 mg/L (table 1). 

Concentrations are lower, and less variable, in water 

sampled from wells in the Central Basin compared 

with the West Coast Basin. Similarly, chloride 

concentrations are low throughout most of the 

freshwater aquifers, commonly less than 50 mg/L. In 

several areas, however, particularly shallow units and 

coastal regions, dissolved-solids concentrations exceed 

500 mg/L and sulfate concentrations exceed 500 mg/L. 

Water is generally under sub-oxic or slightly reducing 

conditions. In some portions of the basin, manganese 

and iron concentrations exceed the drinking-water 

limit. In water from deeper or distal wells (on the basis 

of field observations), hydrogen sulfide gas is inferred 

to be present. 

Dissolved Solids 

Dissolved-solids concentrations, commonly 

referred to as total dissolved solids (TDS), ranged from 

181 to more than 12,000 mg/L (fig. 10A). Water 

throughout much of the Central and West Coast Basins 

contains less than 500 mg/L TDS. In general, TDS 

concentrations decrease with increasing depth and with 

increasing distance from forebay areas. In some 

areas—such as the Whittier Area, near the Palos 

Verdes Hills, and especially along the coast—dissolved 

solids concentrations exceed 1,000 mg/L in wells 

perforated in both the Upper and Lower aquifer 

systems. 

In figure 10B, the median value for TDS is lower 

for water in the Central Basin than for the West Coast 

Basin and lower for water in the Lower aquifer systems 

than for the Upper aquifer systems. The median value 

for TDS in water from wells in the Upper aquifer 

systems of the Central Basin is 443 mg/L. Most water 

in the first quartile of this group is not located in the 

forebay areas, but is similar to native water in the 

Montebello (225-300 mg/L) and Los Angeles 

(275–350 mg/L) Forebays (Poland, 1956). Upgradient 

from the study area in the San Gabriel and San 

Fernando Valleys, water in shallow monitoring wells 

1S/11W-25D1 and 1N/13W-28L1 contained relatively 

low TDS concentrations, 392 and 331 mg/L, 

respectively.

The median value for TDS in water from wells 

perforating the Lower aquifer systems of the Central 

Basin is 359 mg/L (fig. 10B). Some of the lowest 

observed TDS concentrations in the study area occur in 

the Central Basin Pressure Area, particularly in the 

Lower aquifer systems near Lakewood and Long 

Beach, where concentrations are as low as 181 mg/L 

(4S/12W-5H5). High outlying concentrations in wells 

in the Central Basin represent water sampled from 

wells in the Whittier Area (3S/11W-2K4 and 2K5) or 

near the coast (5S/12W-1E1, 4S/12W-25G5). 
28 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California Table 1. Composition of selected waters in the study area, Los Angeles County, California—Continued Shallow1 Forebay1 Native1 Coastal1 Pico unit1 Surface water Imported water4 Gar- dena-1 (3S/14W- 13J8) Lake- wood-1 (4S/12W- 5H10) Hunting- ton Park-1 (2S/13W- 22C2) Rio Hondo-1 (2S/12W- 26D12) Carson-1 (4S/13W- 9H10) Long Beach-1 (4S/12W- 25G3) Haw- thorne-1 (3S/14W- 17G5) Wilming- ton-1 (4S/13W- 28A6) Pico Rivera-1 (2S/11W- 18C4) Com- merce-1 (2S/12W- 7J1) Sea- water2 San Gabriel River3 State Project Colorado River Specific conductance, μS/cm at 25oC 1,665 1,133 581 764 392 317 939 4,430 582 21,700 50,000 528 446 1,070 pH 7.3 7.4 7.8 7.5 8.2 8.8 7.8 7.6 8.0 7.5 — 7.5 8.1 8.3 Temperature, oC 22 21 20 19 24 22 25 22 23 22 — — — 145 Dissolved oxygen, in mg/L 5 .4 .5 .3 .2 <.1 .2 .1 .05 <.1 — — — 105 Alkalinity as CaCO3, in mg/L 161 195 178 146 169 119 442 142 284 503 116 88 75 130 Residue on evaporation, in mg/L 1,160 739 363 484 230 209 549 2,703 370 12,820 34,500 331 246 679 MAJOR IONS, in mg/L Calcium 150 143 59 75 32 4 34 282 8 183 410 43 20 81 Magnesium 37 14 14 14 7 .0 21 96 3 144 1,350 12 12 30 Sodium 87 52 40 62 42 66 143 457 119 4,284 10,500 41 48 101 Potassium 5.4 4.5 3.4 4.0 2.4 .7 14 13 4.7 45 390 5.5 2.7 4.3 Chloride 370 210 22 69 21 12 50 1,209 4 7,071 19,000 51 64 87 Fluoride .30 .16 .47 .45 .26 .66 .24 <.10 .31 .19 1.30 .21 .13 .35 Sulfate 53 44 82 121 <.1 15 1 288 5 4 2,700 77 40 292 Bromide 1.0 1.4 .11 .11 .078 .018 .11 4.6 .011 44 67 — .21 .083 Iodide .009 .089 .004 .020 .027 .009 .077 .79 .005 9.4 .060 — — .0015 Silica as SiO2 29 24 22 22 22 20 34 26 30 31 6.4 — 14 8.6 NUTRIENTS, in mg/L Ammonia as N .090 .50 <.020 <.020 .37 .17 2.4 2.2 2.0 27 — .95 — Nitrite plus nitrate as N 2.0 <.050 .11 2.9 <.050 <.050 <.050 .12 <.050 .029 — 2.17 1.92 .75 Table 1. Orthophosphate as P 1.2 .21 .28 .028 .026 1.6 .22 .10 2.6 .86 .39 .39 — Composition of selected waters in the study area, Los Angeles County, California [USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter; <, less than; —, no data]
Geochemical Analysis 29

1From ‘Geologic, hydrologic, and water-quality data from multiple-well monitoring sites in the Central and West Coast Basins, Los Angeles County, California’ by Land, Everett, and Crawford, 

2002, U.S. Geological Survey Open-File Report 01-277.

2From ‘Study and interpretation of the chemical characteristics of natural water, 3d ed’ by Hem, 1989, U.S. Geological Survey Water-Supply Paper 2254.3From Los Angeles County Public Works, Watershed Management Division, Storm Water Quality Monitoring Report (http://www.ladpw.org/wmd/). Mean concentrations for the San Gabriel River 

(S14) Mass Emission Site, 1994–2000, accessed April 2002.

4Mean concentration for State Project [Devil’s Canyon Afterbay (1974–2001)] and Colorado River water [Lake Mathews Headworks (1942–2001)], Hsiao Chiu Wang, Metropolitan Water District, 

written commun., 2002.

5USGS unpublished data (http://waterdata.usgs.gov/nwis/); sample collected at the Metropolitan Water District, West Basin, Cross-connection #37 on March 17, 1999 (Station ID: 

TRACE ELEMENTS, in 

334921118134101).

μg/L

Barium 100 337 70 64 39 1 34 121 15 621 20 53 — 935

Boron 117 91 133 202 102 88 486 221 603 6,532 4,500 200 160 124Iron 5 145 <3 <10 7 <10 38 17 36 1,049 3 561 — <105Lithium 14 — <4 <4 5 5 12 — 34 148 170 — —Manganese 54 442 9 17 18 12 72 51 40 157 2 79 — <35Strontium 1,200 1,331 470 476 369 25 415 3,688 122 4,227 7,975 — — 9185ISOTOPESDeuterium, in per mil −42 −52 −47 −60 −47 −57 −46 −78 −65 −34 0 — — −985Oxygen-18, in per mil −6.5 −7.8 −7.2 −8.4 −7.3 −8.6 −7.1 −9.8 −9.6 −5.9 0 — — −12.15Tritium, in TU 1.0 2.4 <.1 8.2 <.1 <.1 <.1 19 <.1 .3 — — — 115

Table 1. Composition of selected waters in the study area, Los Angeles County, California—Continued

Shallow1 Forebay1 Native1 Coastal1 Pico unit1 Surface water Imported water4

Gardena-1 

(3S/14W13J8)

Lakewood-1 

(4S/12W5H10)

Huntington 

Park-1 

(2S/13W22C2)

Rio 

Hondo-1 

(2S/12W26D12)

Carson-1 

(4S/13W9H10)

 Long 

Beach-1 

(4S/12W25G3)

Hawthorne-1 

(3S/14W17G5)

Wilmington-1 

(4S/13W28A6)

Pico 

Rivera-1 

(2S/11W18C4)

Commerce-1 

(2S/12W7J1)

Seawater2 San Gabriel River3 State Project Colorado River
30 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Gabriel

San

Rio Hondo

Ballona Creek

River

Los

River

Angeles

Gabriel

River San

Rio

Hondo

Los

River

Angeles

R15W R14W R13W R12W R11W

T5S T4S T3S T2S T1S

West 

Coast

Basin

Barrier

Project

Dominguez Gap Barrier

Project

Alamitos Gap

Barrier Project

430

282

345 544

750

12,600

448 235

564

552

552

219

427

458

4,090

4,090

 500 - 1,000

Greater than

 1,000

6,380

331

392

637

561

399

428

377

504

258

419, 359

212

204

215

240, 210

416

248

248 Less than 500

259

441

358

712

493

373

411

353

479

484

304

208

236

486

500

358

380

312

325

351

478

297

418

457

475

5H5-10 1N3-8

8J1-4

28A3-7

26A2-7

32F1-5

9H9-12

9J1-6

9D1-5

26D9-14

25G3-8

26E2-6

5P9-14

25G1-6

2K4-8

7J1-6

22C1-5

6B4-8

17F1-5

13J5-8

28M3-7

26N3-6

17G3-8

18C4-7

Total dissolved solids

(TDS) concentration – 

In milligrams per liter 

Color Range of values

Production well and number – Wells with perforations located in the:

Other well and number – Wells with perforations located in the:

0 5 MILES

0 5 KILOMETERS

EXPLANATION

San Gabriel Valley

Pacific Ocean

Santa

Monica

Bay

San Pedro Bay

18° 25' 20' 05' 15' 10' 118° 00'

50'

33° 45'

55'

34° 05'

34° 00'

32F1-5

Repetto Hills

Elysia

H

n

ills

Merced Hills

Puente Hills

Santa Monica Mountains

Unconsolidated deposits

Consolidated deposits

Spreading grounds

Seawater barrier project

West Coast Basin

Central Basin

Hollywood Basin

Santa Monica

Basin

Montebello

Forebay

Los Angeles

Forebay

A

USGS multiple-well monitoring site and number – Dashed line 

indicates sites sampled for dissolved solids (see facing page)

Whittier

Area

Upper aquifer systems Lower aquifer systems

Upper aquifer systems Lower aquifer systems

Model subareas

Model boundary

Whittier

Narrows

Los Angeles

Narrows

Dominguez Gap

Palos Verdes Hills

Figure 10. Distribution of dissolved-solids concentrations from sampled ground water (A) and boxplot of concentrations in ground water from the Upper 

and Lower aquifer systems, in the Central and West Coast Basins (B), Los Angeles County, California.
Geochemical Analysis 31

552

4,090

 500 - 1,000

Greater than

 1,000

248 Less than 500

Name on top is 

common name

Boundary between

Upper and Lower

aquifer systems,

where present

Boundary between

Lower aquifer systems 

and Pico unit, where

present

Well perforation

No data

Aquifer systems grouping

for geochemical analysis

Upper Lower Pico unit

Total dissolved-solids

(TDS) concentration –

In milligrams per liter

EXPLANATION

USGS mulitple-well

monitoring site and

abbreviated number –

Color Range of values

A3

A4

A6

A7

H12

N3 H5

G1

P9

P10

P11

P12

P13

P14

G2

G3

G4

G5

G6

H6

H7

H8

H9

H10

N4

N5

N6

N7

N8

H11

H10

H9

A7

A6

A5

A4

A3

A2

A5

F1

F2

F4

F5

F3

M3

M4

N6

N5

N4

N3

F1

F2

C1

J1

D9

C4

G3

G4

G5

G6

G7

G8

C5

C6

C7

D10

D11

D12

D13

D14

J2

J3

J4

J5

J6

C2

C3

C4

C5

F3

F4

F5

M6

M7

M5

G3

J5

J1

B4

B5

B6

B7

B8

J6

J5

J4

J3

J2

J1

D1

D2

E2

E3

E4

K4

K5

K8

K6

K7

E5

E6

D3

D4

D5

J2

J3

J4

J6

J7

J8

G4

G5

G6

G7

G8

490

787

2,470

789

574

1,190

840

293

248

280

200

320

230

206

1,720

515

1,370

1,990

9,760 --

1,110

686

715

844

 300

335

610

256

278

247

206

181

742

1,630

232

196

208

202

278

274

278

308

263

282

--

--

492 669

678

1,490

2,390

2,540

429

326

264

359

771

826

781

--

211

344

482

529

519

811

308

--

447

477

413

977

347

332

319

311

325

324

369

2,060

558

484

564

765

879

4,340

--

624

921

--

641

462

377

373

351

293

1,480

1,640

861

--

384

556

504

457

486

280

446

450

467

355

341

12,200

658

466

353

341

577

649

307

362

455

523

494

547

503

524

Lomita-1 Wilmington-1 Carson-1 Long Beach-2 Long Beach-1 Cerritos-1 Wilmington-2 Lakewood-1

Hawthorne-1 Willowbrook-1 South Gate-1 Downey-1 La Mirada-1 Whittier-1 Gardena-1 Santa Fe Springs-1

Inglewood-1 Los Angeles-1 Huntington Park-1 Commerce-1 Pico Rivera-1 Pico Rivera-2 Inglewood-2 Rio Hondo-1

-26A2-7 -32F1-5 -9H9-12 -1N3-8 -5H5-10 -5P9-14

-17G3-8 -13J5-8 -8J1-4 -6B4-8 -9J1-6 -9D1-5 -26E2-6 -2K4-8

-28M3-7 -26N3-6 -17F1-5 -22C1-5 7J1-6 26D9-14 18C4-7 25G3-8

-28A3-7 -25G1-6

A, continued

Figure 10.—Continued.
32 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Central Basin

Lower

aquifer

systems

Lower

aquifer

systems

Upper

aquifer

systems

Upper

aquifer

systems

West Coast Basin

Pico Unit

Central and

West Coast

Basins

100

1,000

10,000

20,000

TOTAL DISSOLVED-SOLIDS, IN MILLI GRAMS PER LITER

B

(85)

(30)

(30)

Median

EXPLANATION

75th percentile

Number of wells

sampled

Data value less than 

or equal to 1.5 times the 

interquartile range 

outside the quartile

Data value more than or 

equal to 1.5 times the

interquartile range 

outside the quartile

Data value less than or 

equal to 3, and more than 

1.5 times the interquartile

range outside the quartile

25th percentile

(36)

(11)

(6)

Figure 10.—Continued.
Geochemical Analysis 33

In the West Coast Basin, the median value for 

TDS in water from wells perforating the Upper aquifer 

systems is 843 mg/L (fig. 10B). All of these wells 

exceed the Secondary Maximum Contaminant Level 

(SMCL) of 500 mg/L for TDS set by the 

U.S. Environmental Protection Agency 

(U.S. Environmental Protection Agency, 1996). The 

median value for TDS in the Lower aquifer systems of 

the West Coast Basins is 534 mg/L. In general, TDS 

concentrations are lower in the interior part of the basin 

near the NIU, and appear to increase toward the coast. 

Most wells in the first quartile of this group cluster near 

Dominguez Gap (fig. 10A)(such as 4S/13W-9H9; 

207 mg/L). High outlying values in the West Coast 

Basin group are commonly found for wells located 

near the coast, such as 4S/14W-9D1 and 4S/13W27E2. Water from all wells at Inglewood-1 and 

Lomita-1 monitoring sites exceed the SMCL.

Dissolved-solids measurements from the Pico 

unit are limited and vary with respect to depth and 

location. For example, in the relatively shallow portion 

of the Pico unit, wells 2S/11W-18C4 and 4S/13W-1N3 

yield relatively fresh water (362 and 200 mg/L, 

respectively) (fig. 10B). In the relatively deeper portion 

of the Pico unit, however, wells 2S/12W-7J1 and 

2S/14W-28M3 yield relatively saline water (12,200 

and 4,340 mg/L, respectively). These results are 

consistent with earlier observations in the basin (Piper 

and Garrett, 1953; Zielbauer and others, 1962). 

General Chemical Character

The major-ion data for all ground-water samples 

collected for this study are summarized in the trilinear 

diagrams in figure 11. Piper and Garrett (1953) used 

trilinear diagrams to study the occurrence of native, 

blended, and contaminated ground water in earlier 

investigations of the Los Angeles area. The diagram 

shows the relative contribution of major cations and 

anions (on a charge equivalent basis) as a percentage of 

the total ion content of the water (Piper, 1944). In this 

report, the dominant cation and anion species are used 

to describe the chemical character—or hydrochemical 

facies (Knobel and others, 1998)—of a water sample. 

Where no one species exceeds 50 percent, the first and 

second most abundant ions are given for description 

purposes. For example, water from well 4S/13W-28A6 

is termed a sodium/calcium-chloride type. 

Major ion data in figure 11A is grouped 

according to TDS concentrations. Water containing 

more than 1,000 mg/L TDS is characterized principally 

by sodium and chloride ions. Water containing 

dissolved solids from 500 mg/L to 1,000 mg/L displays 

a mixed composition, typically a calcium-bicarbonate 

or calcium/sodium-bicarbonate/chloride character. 

Water containing less than 500 mg/L TDS shows the 

broadest range of chemical composition, collectively a 

calcium-bicarbonate/sulfate to calcium-bicarbonate to 

sodium-bicarbonate character. Of this group, water 

dominated by sodium and bicarbonate ions is located 

away from the forebay area and generally is lower in 

TDS.

Major ion data in figure 11B is grouped 

according to depth. Distinct ground-water 

compositions are not always exclusive to a particular 

aquifer system, or region. In general, wells yielding 

water of calcium-bicarbonate or calciumbicarbonate/sulfate composition are perforated in the 

Upper aquifer systems or are located in or near the 

forebay areas. Wells yielding water of calcium/sodiumbicarbonate or sodium-bicarbonate composition 

typically are perforated in the Lower aquifer systems or 

are located away from areas of recharge. Wells 

perforated in the Pico unit, with the exception of 

2S/12W-7J1 (Commerce-1; see fig. 11C), also yielded 

water of sodium-bicarbonate composition. Wells 

yielding water of sodium-chloride composition are 

located near the coast and are perforated in the Upper 

or Lower aquifer systems.

Central Basin

Historically, the main sources of water in the 

Montebello Forebay were the San Gabriel River and 

Rio Hondo, subsurface flow through the Whittier 

Narrows, and local precipitation. Water currently 

utilized for spreading consists of seasonally varying 

proportions of local runoff, imported water [Colorado 

River and (or) State Water Project], and, increasingly, 

reclaimed water. Values for dissolved solids in the 

Montebello Forebay are considerably higher now than 

during the 1930s and 1940s (typically less than 

300 mg/L; Poland and others, 1956, 1959), suggestive 

of the long-term effects of artificial-recharge 

operations.
34 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

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60 60

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20 20

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60

100

0 0

A

B

Central and West Coast Basins

Central and West Coast Basins

EXPLANATION

SODIUM PLUS POTASSIUM

SULFATE PLUS CHLORIDE

PERCENT

PERCENT

CALCIUM

MAGNESIUM

CHLORIDE, FLUORIDE, NITRITE PLUS NITRATE

SULFATE

CALCIUM PLUS MAGNESIUM

PERCENT

80

60

100

40

20

0

SODIUM PLUS POTASSIUM

SULFATE PLUS CHLORIDE

PERCENT

PERCENT

CALCIUM

MAGNESIUM

CHLORIDE, FLUORIDE, NITRITE PLUS NITRATE

SULFATE

CALCIUM PLUS MAGNESIUM

PERCENT

EXPLANATION

CARBONATE PLUS BICARBONATE

CARBONATE PLUS BICARBONATE

●

Upper aquifer systems

Lower aquifer systems

Pico unit

●

●

● Greater than 1,000

Dissolved solids

concentration – In milligrams

per liter

Less than 500

● 500 – 1,000

●

Figure 11. General chemical character of ground water sampled in the Central and West Coast Basins with grouping by total dissolved solids concentration 

(A), grouping by aquifer systems (B), and labelling of selected wells (C), Los Angeles County, California.
Geochemical Analysis 35

2S/11W-18C4

2S/11W-18C5

2S/12W-26D9

2S/12W-31H2

2S/13W-11R4

2S/13W-17F1

2S/13W-17F2

2S/13W-17F5

2S/13W-22C2

2S/13W-22C4

2S/13W-31C3

3S/11W-19E2

3S/11W-2K4

3S/11W-2K7

3S/12W-14F1

3S/12W-6B4

3S/12W-6B6

3S/12W-6B7

3S/12W-9J1

3S/12W-9J3

3S/12W-9J4

3S/12W-9J5

3S/13W-10L3

3S/13W-8J1

3S/13W8J2

4S/12W-25E1

4S/12W-25G1

4S/12W-25G2

4S/12W-25G3

4S/12W-25G5

4S/12W-28H1

4S/12W-5H9

4S/12W-5H10

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

2S/14W-31H1

3S/14W-13J5

3S/14W-13J6

3S/14W-13J7

3S/14W-13J8

3S/14W-21M1

3S/14W-22L1

4S/13W-15A11

4S/13W-28A3

4S/13W-28A4

4S/13W-32F3

4S/13W-9H9

4S/13W-9H10

4S/13W-9H11

4S/14W-15N1

4S/14W-2N1

4S/14W-2N2

A.

B.

C.

D.

E.

F.

G.

H.

I.

J.

K.

L.

M.

N.

O.

P.

Q.

STATE WELL NUMBERS FOR SELECTED 

WELLS SHOWN IN FIGURES 11A AND B

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B

C

D

E

F

G

I

J

K

L

H

N

M

O

P

Q

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

31

30

32

33

C

80

100

60

40

20

0

20

0

40

60

80

100

80

100

60

20

40

0

20

0

40

80

60

100

SODIUM PLUS POTASSIUM

SULFATE PLUS CHLORIDE

CALCIUM PLUS MAGNESIUM

CARBONATE PLUS BICARBONATE

Figure 11.—Continued.
36 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Data from the Pico Rivera-1 and Rio Hondo-1 

(2S/11W-18C4–7 and 2S/12W-26D9–14, respectively) 

monitoring sites show significant differences in 

chemical character with depth (fig. 11). Calciumbicarbonate/sulfate type water, common in the Upper 

aquifer systems, was not observed in parts of the Lower 

aquifer systems or the Pico unit. In other parts of the 

Lower aquifer systems, such as 2S/11W-18C5 

(307 mg/L TDS), calcium-bicarbonate water is present 

(fig. 11). Farther downgradient, water yielded by 

2S/12W-26D9 (280 mg/L TDS, the lowest observed 

value in the Montebello Forebay) grades to a 

calcium/sodium-bicarbonate composition. Water from 

well 2S/11W-18C4 (362 mg/L TDS) had a strongly 

sodium-bicarbonate character typical of most water 

from the Pico unit. 

As noted earlier, the Los Angeles Forebay differs 

from the Montebello Forebay in that there is no 

artificial ground-water recharge program in place. 

Changes in chemical character, though more subtle, 

occur with depth and reflect this difference. Water 

from the Lower aquifer systems (wells 2S/13W-17F2, 

2S/13W-22C2) has a calcium-bicarbonate character 

and is relatively low in TDS (373, 353 mg/L, 

respectively); in deeper parts (well 2S/13W-11R4) 

water has a calcium/sodium-bicarbonate character. 

Water observed at these locations resembles native 

water of the Los Angeles Forebay as described by 

Poland and others (1956, 1959) in terms of overall 

chemical composition and range of dissolved solids. In 

contrast, relatively shallow monitoring wells at the Los 

Angeles-1 (2S/13W-17F5; 641 mg/l TDS) and 

Huntington Park-1 (2S/13W-22C4; 658 mg/L TDS) 

sites indicate calcium-bicarbonate/chloride and 

calcium-bicarbonate/sulfate water, respectively, is 

present. A possible explanation for these differences 

might be a long-term shift or degradation in the water 

quality of the Los Angeles River.

In the Central Basin Pressure Area, 

calcium/sodium-bicarbonate water is commonly 

present downgradient of the Los Angeles Forebay 

(wells 3S/13W-8J2, 3S/13W-10L3, 2S/13W-31C3, and 

2S/12W-31H2) but is limited to a few deep wells 

downgradient of the Montebello Forebay (3S/12W6B4, 3S/12W-9J1). This water is relatively low in TDS 

(211–377 mg/L) and is quite similar to native water 

described by Poland (1959). Most wells sampled 

downgradient from the Montebello Forebay yielded 

calcium-bicarbonate/sulfate water (3S/12W-6B6–7, 

3S/12W-9J3–5, 3S/12W-14F1, and 3S/11W-19E2) 

containing 447–529 mg/L TDS (fig. 10A, 11).

In the Whittier Area, data collected from the 

Whittier-1 monitoring site indicate water is generally 

higher in dissolved solids than elsewhere in the Central 

Basin; TDS values increase significantly with depth 

(see fig. 10A). The chemical character within the 

Lower aquifer systems grades with depth from mixed 

cation-bicarbonate (3S/11W-2K7) to sodium-sulfate 

(3S/11W-2K4). This sulfate-rich water was not 

observed elsewhere in the study area.

Further downgradient in the Central Basin 

Pressure Area, nearly all wells sampled, especially 

those at the Lakewood-1 (4S/12W-5H59) monitoring 

site, contained water that ranges from a calciumbicarbonate to calcium/sodium-bicarbonate to sodiumbicarbonate composition. Calcium-rich water from this 

group differs from the calcium-rich water in (or near) 

the Montebello Forebay in that dissolved sulfate and 

dissolved solids are relatively low. Additionally, the 

ratio of calcium to sodium generally decreases with 

depth. Monitoring wells (4S/12W-25G1–3) at the Long 

Beach-1 site and a few nearby production wells 

(4S/12W-25E1 and 4S/12W-28H1) perforating Lower 

aquifer systems yielded sodium-bicarbonate water that 

was notably warm, tan-yellow colored, and among the 

lowest in TDS (196–212 mg/L).

In the Central Basin Pressure Area, water in parts 

of the Upper aquifer systems is distinguished as having 

a calcium-chloride character. At well 4S/12W-5H10 

(Lakewood-1 #6; 610 mg/L TDS) (fig. 10A), this 

composition likely results from local recharge to the 

Upper aquifer systems. In comparison, a similar 

chemical character at well 4S/12W-25G5 (Long 

Beach-1 #5; 1,630 mg/L TDS) is attributed to an influx 

of seawater or other brine water. 
Geochemical Analysis 37

West Coast Basin

The chemical character of water in the West 

Coast Basin varies considerably with respect to depth 

and distance from the coast. In the interior of the West 

Coast Basin, as in the Central Basin, TDS content 

generally decreases with depth. Calcium/sodiumchloride water from Gardena-1 (3S/14W-13J8), 

perforating the Upper aquifer systems, contained 

977 mg/L TDS. Data collected from wells at the 

Gardena-1 and Carson-1 (3S/14W-13J7, 

4S/13W-9H11, respectively) monitoring sites indicate 

that the top part of the Lower aquifer systems contains 

calcium-bicarbonate water, also low in TDS (325 and 

320 mg/L, respectively) (fig. 10A). The chemical 

composition of this water is similar to that of several 

upgradient wells (especially at the Willowbrook-1 site) 

across the NIU. At greater depths in the Lower aquifer 

systems, the composition of water shifts from 

calcium/sodium-bicarbonate (4S/13W-9H10 and 

4S/13W-13J6) to sodium-bicarbonate (4S/13W-9H9 

and 4S/13W-17D2). The sodium-bicarbonate character 

of water from Gardena-1 #1 (3S/14W-13J5) in the 

lower San Pedro Aquifer system is distinguished from 

other deep water by a moderate sulfide odor and 

significant concentrations of dissolved ammonia 

5.8 mg/L as N), indicating reducing ground-water 

conditions. This water is similar to native water across 

the NIU (3S/13W-8J1) but differs from deep water in 

the Los Angeles Forebay (2S/13W-11R4 and 

2S/13W-17F1).

The chemical character of water near the coast is 

influenced by the variety of water sources, including 

the ocean and the seawater-barrier projects. Wells 

sampled within approximately 4 mi of the coast had 

TDS ranging from 282 to more than 12,600 mg/L. Of 

these, water from wells 4S/14W-2N1–2, and -15N1; 

3S/14W-21M1 and -22L1; 2S/14W-31H1; and 

4S/13W-32F3 is calcium/sodium-bicarbonate to 

sodium-bicarbonate in character with TDS ranging 

from 282 to 544 mg/L. The sodium-bicarbonate water 

noted in well 4S/14W-15N1 (Upper San Pedro Aquifer 

system) is similar to native water observed locally in 

the Silverado aquifer by Poland (1959). Most other 

wells near the coast yield water that is primarily 

comprised of sodium and chloride ions and typically 

exceeds 1,000 mg/L TDS. At the USGS Wilmington-1 

monitoring site, however, wells 4S/13W-28A3 and -

28A4, perforated in the Lower aquifer systems, yielded 

sodium-chloride type water, but with only 490 and 

787 mg/L TDS, respectively (fig. 10A). 

Dissolved Chloride

Dissolved chloride in ground water is generally 

unreactive and attributable to both natural and 

anthropogenic processes. Chloride concentrations in 

water from sampled wells ranged from 4 to more than 

7,000 mg/L (fig. 12). Chloride concentrations correlate 

strongly (R2 = 0.98) with TDS and are higher in wells 

near the coast, near uplifted basin margins, and in 

selected shallow wells. The SMCL for chloride is 

250 mg/L (U.S. Environmental Protection Agency, 

1996).

In the Central Basin, the median chloride value 

for water in the Upper aquifer systems is about 

60 mg/L. In the Lower aquifer systems the median 

value is 30 mg/L. Relatively higher chloride water is 

present in a pair of wells in the Whittier Area 

(3S/11W-2K4 and -2K5; 280 and 240 mg/L, 

respectively) (fig. 12). 

In the West Coast Basin the median chloride 

values for the Upper and Lower aquifer systems are 

300 and 95 mg/L, respectively. Near the coast, water 

from wells 4S/13W-27E2 and -32F5, and 4S/14W-9D1 

contain significant dissolved chloride (3,200, 5,200, 

and 6,800 mg/L, respectively). A two-part mixture 

between native West Coast Basin ground water 

(table 1) and seawater yields partial seawater 

compositions of 17, 27, and 35 percent for these wells. 

However, there may be other sources of high-chloride 

water besides seawater—including water from shallow 

or semi-perched aquifers (Piper and Garrett, 1953), 

water from applied irrigation (Izbicki, 1991), water 

from fine-grained marine deposits, and water from the 

dissolution of evaporite minerals. Chemical data for 

some of these sources are given in table 1.
38 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Gabriel

San

Rio Hondo

River

Los

River

Angeles

Gabriel

River San

Rio

Hondo

Los

River

Angeles

Ballona Creek

R15W R14W R13W R12W R11W

West 

Coast

Basin

Barrier

Project

Dominguez Gap Barrier

Project

Alamitos Gap

Barrier Project

28, 35

20 76

45

6,800

 95 13

2,100

84

6,800

 25-250

Greater than

 250

40

7

70

72

84

3,200

30

61

180, 210

42

58

31

85

22 Less than 25

49, 31

170

50

41

21

69

60

21

6

9

79

75

32

53

23

36

130

22

52 52

60

14

5H5-10 1N3-8

8J1-4

28A3-7

26A2-7

32F1-5

9H9-12

9J1-6

9D1-5

26D9-14

25G3-8

26E2-6

5P9-14

25G1-6

2K4-8

7J1-6

22C1-5

6B4-8

17F1-5

13J5-8

28M3-7

26N3-6

17G3-8

18C4-7

Dissolved chloride

concentration – In

milligrams per liter 

Color Range of values Production well and number – Wells with perforations located in the:

Other well and number – Wells with perforations located in the:

0 5 MILES

0 5 KILOMETERS

EXPLANATION

San Gabriel Valley

Pacific Ocean

Santa

Monica

Bay

San Pedro Bay

18° 25' 20' 05' 15' 10' 118° 00'

32F1-5

Repetto Hills

Elysia

Hills

n

Merced Hills

Puente Hills

Santa Monica Mountains

Unconsolidated deposits

Consolidated deposits

Spreading grounds

Model boundary

Model subareas

Seawater barrier project

West Coast Basin

Central Basin

Hollywood Basin

Santa Monica

Basin

Montebello

Forebay

Los Angeles

Forebay

USGS multiple-well monitoring site and number – Dashed line indicates

sites sampled for chloride (see facing page)

Whittier

Area

T5S T4S T3S T2S T1S

50'

33° 45'

55'

34° 05'

34° 00'

Upper aquifer systems Lower aquifer systems

Upper aquifer systems Lower aquifer systems

Dominguez Gap

Palos Verdes Hills

Whittier

Narrows

Los Angeles

Narrows

Figure 12. Dissolved-chloride concentration in ground water sampled in the study area, Los Angeles County, California.
Geochemical Analysis 39

A3

A4

A6

A7

H12

N3 H5

G1

P9

P10

P11

P12

P13

P14

G2

G3

G4

G5

G6

H6

H7

H8

H9

H10

N4

N5

N6

N7

N8

H11

H10

H9

A7

A6

A5

A4

A3

A2

A5

F1

F2

F4

F5

F3

M3

M4

N6

N5

N4

N3

F1

F2

C1

J1

D9

C4

G3

G4

G5

G6

G7

G8

C5

C6

C7

D10

D11

D12

D13

D14

J2

J3

J4

J5

J6

C2

C3

C4

C5

F3

F4

F5

M6

M7

M5

G3 J5

J1

B4

B5

B6

B7

B8

J6

J5

J4

J3

J2

J1

D1

D2

E2

E3

E4

K4

K5

K8

K6

K7

E5

E6

D3

D4

D5

J2

J3

J4

J6

J7

J8

G4

G5

G6

G7

G8

Upper Lower Pico unit

210

340

1,200

230

120

150

97

29

22

20

21

23

20

20

910

56

510

1,000

5,200 --

510

250

230

340

580

72

210

10

19

10

8

19

130

650

12

12

15

15

11

11

12

20

14

15

--

--

62 80

80

170

240

280

27

16

16

26

160

120

170

--

6

26

66

74

63

94

21

180

50

56

34

370

25

20

21

18

22

21

17

580

190

52

50

43

48

1,600

--

170

300

--

83

42

24

23

22

21

22

74

230

--

61

88

120

73

46

19

50

59

69

58

48

7,100

60

43

22

21

69

84

19

4

59

54

59

94

88

93

Lomita-1 Wilmington-1 Carson-1 Long Beach-2 Long Beach-1 Cerritos-1 Wilmington-2 Lakewood-1

Hawthorne-1 Willowbrook-1 South Gate-1 Downey-1 La Mirada-1 Whittier-1 Gardena-1 Santa Fe Springs-1

Inglewood-1 Los Angeles-1 Huntington Park-1 Commerce-1 Pico Rivera-1 Pico Rivera-2 Inglewood-2 Rio Hondo-1

-26A2-7 -32F1-5 -9H9-12 -1N3-8 -5H5-10 -5P9-14

-17G3-8 -13J5-8 -8J1-4 -6B4-8 -9J1-6 -9D1-5 -26E2-6 -2K4-8

-28M3-7 -26N3-6 -17F1-5 -22C1-5 -7J1-6 -26D9-14 -18C4-7 -25G3-8

-28A3-7 -25G1-6

Name on top is 

common name

Boundary between

Upper and Lower

aquifer systems,

where present

Boundary between

Lower aquifer systems 

and Pico unit, where

present

Well perforation

No data

Aquifer systems grouping

for geochemical analysis

EXPLANATION

USGS mulitple-well

monitoring site and

abbreviated number –

84

6,800

25-250

Greater than

 250

22 Less than 25

Color Range of values

Dissolved chloride

concentration – In

milligrams per liter

Figure 12.—Continued.
40 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Dissolved Oxygen

Dissolved oxygen is supplied to the groundwater system by the infiltration of recharge water and 

by the movement of air throughout the unsaturated 

zone above the water table (Hem, 1992). Surface water 

may contain significant dissolved oxygen, depending 

on the temperature and, to a lesser extent, source. 

Decomposable organic material (especially peat or 

lignite) is abundant in coastal aquifers and will react, in 

the presence of certain bacteria, with dissolved oxygen 

in the ground water (Hem, 1992). In the Central and 

West Coast Basins, dissolved-oxygen concentrations 

range from less than measurable to almost 6 mg/L; 

80 percent of the values are less than 1 mg/L (fig. 13). 

The median value for dissolved oxygen in the 

Upper aquifer systems of the Central Basin is 

0.3 mg/L. In most of the Central Basin, including the 

Los Angeles Forebay, concentrations decrease with 

depth and (or) with increasing distance downgradient 

(fig. 13). In and near the Montebello Forebay, 

however, dissolved-oxygen concentrations appear to 

increase with depth. For example, dissolved oxygen in 

most water collected from the Upper aquifer systems is 

low (less than 1 mg/L). Such concentrations have been 

attributed to the rapid microbial oxidation of nutrientrich reclaimed wastewater (Leenheer and others, 2001) 

that currently averages about one-third of the 

artificially spread water. In contrast, dissolved oxygen 

is much higher in parts of the Lower aquifer systems 

(2S/12W-25G35) and near the Montebello Forebay 

(3S/12W-6B5 and -9J2 and 3S/11W-19E2) (fig. 13). 

Artificial recharge containing a greater percentage of 

imported water during the 1960s may account for these 

higher concentrations. In the distal part of the Central 

Basin Pressure Area, dissolved oxygen is usually low 

or less than measurable (3S/13W-26N5 and 

4S/12W-5H6). 

Dissolved-oxygen concentrations in the West 

Coast Basin are much less variable than those in the 

Central Basin. The median value for water in the Upper 

and Lower aquifer systems is 0.1 mg/L; most wells 

contain concentrations that are less than measurable. 

High outlying values are associated with water from 

relatively shallow wells and may result from the 

infiltration of local precipitation (3S/14W-13J8, 

2S/14W-28M7) or from the injection of imported water 

(4S/13W-28A7) along the coast (fig. 13). 

Dissolved Sulfate

Sulfate, unlike chloride, is not conservative and 

is controlled by redox conditions in the ground-water 

system. Dissolved sulfate in ground water is commonly 

attributed to dissolution of evaporites (for example, 

gypsum) or oxidation of pyrite minerals. Dissolvedsulfate concentrations exceeding 250 mg/L are an 

aesthetic concern (U.S. Environmental Protection 

Agency, 1996) and occur in 7 percent of all wells 

sampled during this study (fig. 14). Locally, sources of 

high-sulfate water include seawater, applied irrigation 

water, and imported Colorado River water (table 1). 

Dissolved-sulfate concentrations range from less 

than measurable (0.1 mg/L) to 1,300 mg/L (fig 14). In 

the Central Basin, the median value for sulfate is 

110 mg/L in the Upper aquifer systems and 74 mg/L 

the Lower aquifer systems; concentrations do not 

always decrease with increasing depth. Sulfate 

concentrations generally decrease away from the 

forebays. In distal parts of the Central Basin Pressure 

Area, the decrease in sulfate concentrations is abrupt 

(see, for example, 2S/14W-26N5, 3S/13W-8J1, and 

4S/12W-5H7, and -1N4) because little or no artificially 

recharged water is present. Very low or less than 

measurable sulfate in the study area is also consistent 

with sulfate reduction, a microbially mediated process 

that occurs in the absence of dissolved oxygen (Piper, 

1953; Drever, 1988). The reduction of dissolved sulfate 

significantly influences water quality in portions of the 

study area.

Very high values of sulfate in the Central Basin 

were measured in water from wells at several depths in 

the Whittier Area (3S/11W-2K45, -2K8) (fig. 14). Near 

the Alamitos Gap Barrier Project, seawater may be a 

source of high sulfate to well 4S/12W-25G5. Other 

locations that exceed the SMCL (250 mg/L) include a 

shallow monitoring well at Downey-1 (3S/12W-9J6) 

and at the Long Beach-2 site along the Los Angeles 

River (4S/13W-1N78), near the NIU. 
Geochemical Analysis 41

THIS PAGE INTENTIONALLY LEFT BLANK
42 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Gabriel

San

Rio Hondo

River

Los

River

Angeles

Gabriel River San

Rio

Hondo

Los

River

Angeles

Ballona Creek

R15W R14W R13W R12W R11W

West 

Coast

Basin

Barrier

Project

Dominguez Gap Barrier

Project

Alamitos Gap

Barrier Project

<.1 <.1

<.1

.4

.6

<.1

1.4

7.6

.8

2.5

0.2 - 0.9

Greater than 0.9

1.4

4.2

.7

1.4

3.4

<.1

.8

.8

1.8 1.2

<.1

.8

2.4

.8

.8

.1

<.1

<.1

4.2

1.2

.1 Less than 0.2

1.6

5H5-10 1N3-8

8J1-4

28A3-7

26A2-7

32F1-5

9H9-12

9J1-6

9D1-5

26D9-14

25G3-8

26E2-6

5P9-14

25G1-6

2K4-8

7J1-6

22C1-5

6B4-8

17F1-5

13J5-8

28M3-7

26N3-6

17G3-8

18C4-7

Dissolved-oxygen

concentration – In

milligrams per liter

Color Range of values

0 5 MILES

0 5 KILOMETERS

San Gabriel Valley

Pacific Ocean

Santa

Monica

Bay

San Pedro Bay

18° 25' 20' 05' 15' 10' 118° 00'

Repetto Hills

Elysia

H

n

ills

Merced Hills

Puente Hills

Santa Monica Mountains

West Coast Basin

Central Basin

Hollywood Basin

Santa Monica

Basin

Montebello

Forebay

Los Angeles

Forebay

T5S T4S T3S T2S T1S

50'

33° 45'

55'

34° 05'

34° 00'

Whittier

Narrows

Los Angeles

Narrows

Dominguez Gap

Whittier

Area

Palos Verdes Hills

Production well and number – Wells with perforations located in the:

Other well and number – Wells with perforations located in the:

EXPLANATION

32F1-5 Unconsolidated deposits

Consolidated deposits

Spreading grounds

Model boundary

Model subareas

Seawater barrier project

USGS multiple-well monitoring site and number – Dashed line 

indicates sites sampled for dissolved oxygen (see facing page)

Upper aquifer systems Lower aquifer systems

Upper aquifer systems Lower aquifer systems

Figure 13. Dissolved-oxygen concentrations in ground water sampled in the study area, Los Angeles County, California.
Geochemical Analysis 43

A3

A4

A6

A7

H12

N3 H5

G1

P9

P10

P11

P12

P13

P14

G2

G3

G4

G5

G6

H6

H7

H8

H9

H10

N4

N5

N6

N7

N8

H11

H10

H9

A7

A6

A5

A4

A3

A2

A5

F1

F2

F4

F5

F3

M3

M4

N6

N5

N4

N3

F1

F2

C1

J1

D9

C4

G3

G4

G5

G6

G7

G8

C5

C6

C7

D10

D11

D12

D13

D14

J2

J3

J4

J5

J6

C2

C3

C4

C5

F3

F4

F5

M6

M7

M5

G3 J5

J1

B4

B5

B6

B7

B8

J6

J5

J4

J3

J2

J1

D1

D2

E2

E3

E4

K4

K5

K8

K6

K7

E5

E6

D3

D4

D5

J2

J3

J4

J6

J7

J8

G4

G5

G6

G7

G8

.2

.2

.2

<.2

.2

.4

.6

 .8

<.1

.2

<.1

.3

.2

<.1

<.2

<.1

<.1

<.1

<.1 --

.1

<.1

<.1

--

.2

<.1

.2

.3

.2

.2

<.1

<.1

.1

.5

.5

<.1

.1

<.1

.2

.2

.3

.6

.2

.2

--

--

.3 1.2

.9

.6

.6

.5

.2

.1

<.1

.1

<.1

<.1

--

--

.2

3.3

3.2

.2

.2

.2

.2

2.5

4.1

.3

.2

6.0

.2

.4

.2

.1

.8

.5

<.1

.2

<.1

.2

.2

<.1

<.1

<.1

--

.2

3.4

--

2.6

.5

--

.4

.4

<.1

<.1

<.1

.1

--

5.7

4.8

.6

.3

<.1

.2

.6

.9

.3

.3

.3

<.1

1.3

1.7

.5

.2

.3

.2

.2

 .1

2.5

3.3

3.5

.1

.2

.1

.9

2.5

 .2 - .9

Greater than

 .9

.1 Less than .2

Dissolved oxygen

concentration –

In milligrams per liter

(mg/L)

Color Range of values

Upper Lower Pico unit

Name on top is 

common name

Boundary between

Upper and Lower

aquifer systems,

where present

Boundary between

Lower aquifer systems 

and Pico unit, where

present

Well perforation

No data

< Less than

Aquifer systems 

grouping for 

geochemical analysis

EXPLANATION

USGS mulitple-well

monitoring site and

abbreviated number –

Lomita-1 Wilmington-1 Carson-1 Long Beach-2 Long Beach-1 Cerritos-1 Wilmington-2 Lakewood-1

Hawthorne-1 Willowbrook-1 South Gate-1 Downey-1 La Mirada-1 Whittier-1 Gardena-1 Santa Fe Springs-1

Inglewood-1 Los Angeles-1 Huntington Park-1 Commerce-1 Pico Rivera-1 Pico Rivera-2 Inglewood-2 Rio Hondo-1

-26A2-7 -32F1-5 -9H9-12 -1N3-8 -5H5-10 -5P9-14

-17G3-8 -13J5-8 -8J1-4 -6B4-8 -9J1-6 -9D1-5 -26E2-6 -2K4-8

-28M3-7 -26N3-6 -17F1-5 -22C1-5 -7J1-6 -26D9-14 -18C4-7 -25G3-8

-28A3-7 -25G1-6

Figure 13.—Continued.
44 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Gabriel

San

Rio Hondo

River

Los

River

Angeles

Gabriel

River

San

Rio

Hondo

Los

River

Angeles

Ballona Creek

R15W R14W R13W R12W R11W

West 

Coast

Basin

Barrier

Project

Dominguez Gap Barrier

Project

Alamitos Gap

Barrier Project

17, 3

73 63

.3

870

 .4 

43

200

 25-250

Greater than

 250

41

15

110

140

230

460

460

23

110

13, 31

110

120

88

120

Less than 25

92

31

31

5

5

100

68

120 130

55

17

26

120

130

74

100

63

25

33

42

110

110

130

.3

80

5H5-10 1N3-8

8J1-4

28A3-7

26A2-7

32F1-5

9H9-12

9J1-6

9D1-5

26D9-14

25G3-8

26E2-6

5P9-14

25G1-6

2K4-8

7J1-6

22C1-5

6B4-8

17F1-5

13J5-8

28M3-7

26N3-6

17G3-8

18C4-7

Dissolved sulfate

concentration – In

milligrams per liter

Color Range of values

0 5 MILES

0 5 KILOMETERS

EXPLANATION

San Gabriel Valley

Pacific Ocean

Santa

Monica

Bay

San Pedro Bay

18° 25' 20' 05' 15' 10' 118° 00'

Repetto Hills

Elysia

Hills

n

Merced Hills

Puente Hills

Santa Monica Mountains

West Coast Basin

Central Basin

Hollywood Basin

Santa Monica

Basin

Montebello

Forebay

Los Angeles

Forebay

Whittier Area

T5S T4S T3S T2S T1S

50'

33° 45'

55'

34° 05'

34° 00'

Whittier

Narrows

Los Angeles

Narrows

Dominguez Gap

Palos Verdes Hills

Production well and number – Wells with perforations located in the:

Other well and number – Wells with perforations located in the:

32F1-5 Unconsolidated deposits

Consolidated deposits

Spreading grounds

Seawater barrier project

USGS multiple-well monitoring site and number – Dashed line 

indicates sites sampled for sufate (see facing page)

Upper aquifer systems Lower aquifer systems

Upper aquifer systems Lower aquifer systems

Model subareas

Model boundary

Figure 14. Dissolved sulfate concentrations in ground water sampled in the study area, Los Angeles County, California.
Geochemical Analysis 45

A3

A4

A6

A7

H12

N3 H5

G1

P9

P10

P11

P12

P13

P14

G2

G3

G4

G5

G6

H6

H7

H8

H9

H10

N4

N5

N6

N7

N8

H11

H10

H9

A7

A6

A5

A4

A3

A2

A5

F1

F2

F4

F5

F3

M3

M4

N6

N5

N4

N3

F1

F2

C1

J1

D9

C4

G3

G4

G5

G6

G7

G8

C5

C6

C7

D10

D11

D12

D13

D14

J2

J3

J4

J5

J6

C2

C3

C4

C5

F3

F4

F5

M6

M7

M5

G3 J5

J1

B4

B5

B6

B7

B8

J6

J5

J4

J3

J2

J1

D1

D2

E2

E3

E4

K4

K5

K8

K6

K7

E5

E6

D3

D4

D5

J2

J3

J4

J6

J7

J8

G4

G5

G6

G7

G8

<.1

59

290

140

110

430

260

46

27

2

.3

62

<.1

<.1

50

<.1

<.1

29

590 --

26

14

13

27

73

<.1

44

14

15

14

15

15

210

280

33

15

.3

2

24

29

37

58

40

49

--

100 170

170

650

1,200

1,300

< Less than

94

58

53

93

90

41

93

--

16

74

130

130

120

260

59

4

110

125

79

53

76

71

71

.7

66

30

1

600

19

.7

1

.7

<.1

4

--

79

100

--

140

110

84

84

69

8

3

11

120

--

40

110

49

68

100

52

120

120

120

87

86

4

200

120

82

80

170

220

65

5

120

130

130

140

130

140

 25-250

Greater than

 250

460

Less than 25

31

5

Upper Lower Pico unit

Dissolved sulfate

concentration – In

milligrams per liter 

Color Range of values

Lomita-1 Wilmington-1 Carson-1 Long Beach-2 Long Beach-1 Cerritos-1 Wilmington-2 Lakewood-1

Hawthorne-1 Willowbrook-1 South Gate-1 Downey-1 La Mirada-1 Whittier-1 Gardena-1 Santa Fe Springs-1

Inglewood-1 Los Angeles-1 Huntington Park-1 Commerce-1 Pico Rivera-1 Pico Rivera-2 Inglewood-2 Rio Hondo-1

-26A2-7 -32F1-5 -9H9-12 -1N3-8 -5H5-10 -5P9-14

-17G3-8 -13J5-8 -8J1-4 -6B4-8 -9J1-6 -9D1-5 -26E2-6 -2K4-8

-28M3-7 -26N3-6 -17F1-5 -22C1-5 -7J1-6 -26D9-14 -18C4-7 -25G3-8

-28A3-7 -25G1-6

Name on top is 

common name

Boundary between

Upper and Lower

aquifer systems,

where present

Boundary between

Lower aquifer systems 

and Pico unit, where

present

Well perforation

No data

Aquifer systems grouping

for geochemical analysis

EXPLANATION

USGS mulitple-well

monitoring site and

abbreviated number –

Figure 14.—Continued.
46 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Sulfate concentrations are relatively low 

throughout most of the West Coast Basin, with median 

values of 100 and 14 mg/L in the Upper and Lower 

aquifer systems, respectively. Concentrations vary 

considerably in the Upper aquifer systems and, along 

the coast, exceed the SMCL (250 mg/L) in water from 

wells 3S/14W-17G8, 4S/14W-9D1, and 4S/13W-27E2. 

In the Lower aquifer systems, less than measurable 

sulfate concentrations occur in water from several 

wells (3S/14W-17G3 and 4S/13W-9H9, -28A3, and 

-32F3). A rotten egg odor, presumed to be hydrogen 

sulfide gas, was observed in water outgassing from 

these and other wells in deep parts of the study area. 

Sulfide, generated as a product of sulfate reduction, 

also is indicative of strongly reducing ground-water 

conditions. 

Dissolved Manganese

Dissolved manganese in the study area generally 

is present as Mn+2 and controlled by the redox 

condition of the ground water (Hem, 1992). 

Concentrations range from less than 1 g/L to more than 

1,000 g/L. About 40 percent of the sampled wells 

yielded water exceeding the SMCL, which is set, for 

aesthetic reasons, at 50 g/L (U.S. Environmental 

Protection Agency, 1996).

The median value for manganese in the West 

Coast Basin (72 g/L) was higher than in the Central 

Basin (30 g/L). The median value for the Upper aquifer 

systems (76 g/L) was higher than in the Lower aquifer 

systems (26 g/L). The data indicate a general pattern of 

increasing concentrations along flowpaths. Relatively 

low (less than 5 g/L) concentrations of manganese 

were found in the forebay areas and in Lower aquifer 

systems wells several miles downgradient from the 

Montebello Forebay. Low manganese concentrations 

are expected under oxic conditions. Relatively high 

(greater than 50 g/L) concentrations of manganese 

were found in most water from the Upper aquifer 

systems outside the forebays and in the Lower aquifer 

systems along the coast, in the Whittier area, and in the 

southeast part of the Central Basin Pressure Area. 

Higher concentrations are expected in the absence of 

dissolved oxygen prior to the reduction of ironoxidized minerals (Berner, 1981). Particularly high 

manganese concentrations were measured in water 

from several wells in the Central Basin (4S/12W-5H8, 

3S/11W-26E5, and 4S/11W-25G5) and the West Coast 

Basin (3S/14W-17G8 and -13J6, and 2S/14W-28M5) 

(fig. 8). 

Dissolved Iron

Iron, like dissolved oxygen and sulfate, is not 

conservative in the ground-water flow system. 

Dissolved iron in ground water is controlled by pH and 

redox conditions and is dependent on iron-bearing 

minerals in the aquifer (Hem, 1992). In the study area, 

concentrations ranged from less than 3 g/L to more 

than 1,000 g/L. The SMCL for dissolved iron is set at 

300 g/L (U.S. Environmental Protection Agency, 

1996). 

Iron exceeded the limit in only 6 percent of all 

measured samples. These samples were collected from 

wells near the coast (4S/13W-27E2 and 4S/14W-2N4), 

in deep portions of the Whittier area (3S/11W-2K4–5), 

or in the Pico unit (2S/14W-28M3 and -26N3, and 

2S/12W-7J1) (fig. 8).

The median value for iron in wells sampled in 

the West Coast Basin was 38 g/L; concentrations 

generally were more variable in the Upper aquifer 

systems than in the Lower aquifer systems. The median 

value in the Central Basin was 22 g/L; higher 

concentrations (30–300 μg/L) were found in portions 

of the Upper aquifer systems.

Isotopic Composition of Ground Water

Isotopes help yield interpretations that may not 

be apparent from traditional chemical or hydrologic 

data. In this study, isotopes were used to evaluate the 

source of ground-water recharge, ground-water 

movement, and relative residence time of water within 

the aquifer systems in the study area.

Deuterium and Oxygen-18 

Oxygen-18 and deuterium (hydrogen-2) are 

stable isotopes of oxygen and hydrogen. These isotopes 

are heavier than the common oxygen and hydrogen 

isotopes (oxygen-16 and hydrogen-1, respectively) 

and, as a result, show slightly different physical and 

chemical behavior. 
Geochemical Analysis 47

The isotopic composition of water is measured 

as a ratio (for example, oxygen-18/oxygen-16 or 

deuterium/hydrogen) and is expressed in terms of per 

mil (parts per thousand) differences (delta oxygen-18, 

δ18O, or delta deuterium, δD) from the international 

standard composition of ocean water, known as Vienna 

Standard Mean Ocean Water (VSMOW) (Gonfiantini, 

1984). Differences are computed as: 

By convention, VSMOW has δD and δ18O 

values equal to 0.0 per mil. Water that has an isotopic 

ratio less than VSMOW will have a negative δD value 

and is depleted in deuterium relative to the ocean-water 

standard. 

The δD values for all wells sampled in the study 

area are shown in figure 15. δD values ranged from 

-34 per mil (near the West Coast Basin barrier project) 

to -88 per mil (near the Alamitos Gap Barrier Project). 

Isotopically light water (δD more negative than -50 per 

mil) was generally observed in the eastern half of the 

study area; isotopically heavy water (δD less negative 

than -50 per mil) was observed in the western half of 

the study area. Isotopic fractionation and mixing are 

two processes that affect the stable-isotope 

composition of ground water. 

Changes to δD and δ18O of water as a result of 

isotopic fractionation typically occur prior to recharge. 

When water evaporates or condenses, slight differences 

in mass preferentially cause more of the lighter 

isotopes to partition into the less dense phase. These 

changes do not readily occur in low-temperature 

ground-water systems. Changes to δD and δ18O of 

water as a result of mixing require two or more 

isotopically distinct sources of water. δD and δ18O are 

conservative in mixing; a binary mixture will therefore 

produce an isotopic composition proportional to each 

source.

Since most precipitation in the study area 

originates from evaporation of seawater, δD and δ18O 

values of precipitation are linearly correlated and can 

be plotted along a line referred to as the meteoric water 

line (Craig, 1961). In figure 16A, as one moves up the 

meteoric water line, one moves from isotopically 

lighter water (more negative δD and δ18O) to 

isotopically heavier water (less negative δD and δ18O). 

The isotopic composition of samples relative to each 

other and to the meteoric water line provides 

information on source and evaporative effects of the 

water (Mazor, 1991; Izbicki, 1996). 

The isotopic composition of precipitation is 

highly variable and dependent on meteorological 

factors including—air mass source, temperature, 

elevation, proximity to the coast, and rainout effects 

(Williams and Rodini, 1997; Kendall and McDonnell, 

1998). Large, short-term variations in the isotopic 

composition of precipitation (which becomes groundwater recharge) are eventually dampened by dispersion 

within the ground-water system yielding a wellaveraged composition that relates to a particular source 

of recharge (Clark and Fritz, 1997). On a regional 

scale, water condensing at cooler temperatures (or 

higher elevations) is isotopically lighter then water 

condensing at warmer temperatures (or lower 

elevations).

In figure 16A, δD and δ18O data for sampled 

wells indicate that a range of isotopic compositions is 

present in both ground-water basins. Most ground 

water ranges from -37 to -64 per mil δD. Imported 

Colorado River and State Project water sampled as part 

of this study has a lighter isotopic composition (about 

-100 and -73 per mil δD, respectively) and plots 

substantially below the meteoric water line (fig. 16A) 

due to extensive evaporation (Williams and Rodini, 

1997).

Central Basin

In the Central Basin, δD for water in sampled 

wells ranged from -34 to -88 per mil (fig. 16). Most 

samples having an isotopic composition that plots 

above the meteoric line cluster into two groups of 

values based on geographic regions within the basin. 

These differences indicate that, historically, separate 

sources of recharge have existed for each forebay in the 

Central Basin.

Ratiosample Ratio { } ( ) ⁄ VSMOW – 1 ⋅ 1 000 ,
48 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Gabriel

San

Rio Hondo

River

Los

River

Angeles

Gabriel

River

San

Rio

Hondo

Los

River

Angeles

Ballona Creek

R15W R14W R13W R12W R11W

West 

Coast

Basin

Barrier

Project

Dominguez Gap Barrier

Project

Alamitos Gap

Barrier Project

-48, -48

-49 -40

-48

-34

-48

-55

-88

-45

-52

-53

-54

-61

-52

-62

-40

-51

-44, -47

-62 Less than -50

-61

-58

-51

-61

-55

-47 -47

-58

-57

-52

-59

-47

-48

-48

-60

-48

-57

-58

-47

-58

-47

-60

-58

-47

-56 -53

-64

-61

-56

-63

-56

-46

-44

-49

-63

-59

-61

-48 Greater than

or equal to -50

-51

5H5-10 1N3-8

8J1-4

28A3-7

26A2-7

32F1-5

9H9-12

9J1-6

9D1-5

26D9-14

25G3-8

26E2-6

5P9-14

25G1-6

2K4-8

7J1-6

22C1-5

6B4-8

17F1-5

13J5-8

28M3-7

26N3-6

17G3-8

18C4-7

0 5 MILES

0 5 KILOMETERS

EXPLANATION

San Gabriel Valley

Pacific Ocean

Santa

Monica

Bay

San Pedro Bay

18° 25' 20' 05' 15' 10' 118° 00'

Repetto Hills

Elysia

H

n

ills

Merced Hills

Puente Hills

Santa Monica Mountains

West Coast Basin

Central Basin

Hollywood Basin

Santa Monica

Basin

Montebello

Forebay

Los Angeles

Forebay

Delta deuterium ratios

 – In per mil

Color Range of values

Whittier

Area

T5S T4S T3S T2S T1S

50'

33° 45'

55'

34° 05'

34° 00'

Palos Verdes Hills

Whittier

Narrows

Los Angeles

Narrows

Dominguez Gap

Production well and number – Wells with perforations located in the:

Other well and number – Wells with perforations located in the:

32F1-5 Unconsolidated deposits

Consolidated deposits

Spreading grounds

Seawater barrier project

USGS multiple-well monitoring site and number – Dashed line 

indicates sites sampled for delta-deuterium (see facing page)

Upper aquifer systems Lower aquifer systems

Upper aquifer systems Lower aquifer systems

Model subareas

Model boundary

Figure 15. Delta-deuterium values in ground water sampled in the study area, Los Angeles County, California.
Geochemical Analysis 49

-62 Less than -50

-48 Greater than

or equal to -50

Color Range of values

Delta-deuterium – In

 per mil

A3

A4

A6

A7

H12

N3 H5

G1

P9

P10

P11

P12

P13

P14

G2

G3

G4

G5

G6

H6

H7

H8

H9

H10

N4

N5

N6

N7

N8

H11

H10

H9

A7

A6

A5

A4

A3

A2

A5

F1

F2

F4

F5

F3

M3

M4

N6

N5

N4

N3

F1

F2

C1

J1

D9

C4

G3

G4

G5

G6

G7

G8

C5

C6

C7

D10

D11

D12

D13

D14

J2

J3

J4

J5

J6

C2

C3

C4

C5

F3

F4

F5

M6

M7

M5

G3

J5

J1

B4

B5

B6

B7

B8

J6

J5

J4

J3

J2

J1

D1

D2

E2

E3

E4

K4

K5

K8

K6

K7

E5

E6

D3

D4

D5

J2

J3

J4

J6

J7

J8

G4

G5

G6

G7

G8

-47

-45

-76

-74

-47

-42

-42

-49

-51

-61

-64

-47

-47

-48

-48

-60

-56

-51

-58 --

-41

-45

-50

-43

-42

-51

-52

-53

-52

-53

-53

-59

-53

-65

-57

-57

-57

-57

-53

-52

-55

-53

-53

-56

--

--

-52 -37

-37

-41

-41

-43

-54

-55

-55

-53

-50

-44

-49

--

-54

-57

-68

-59

-53

-55

-48

-59

-61

-59

-48

-45

-50

-47

-47

-50

-47

-47

-53

-51

-45

-46

-46

-49

-51

-50

--

-39

-41

--

-48

-47

-48

-47

-49

-49

-62

-60

-41

--

-40

-57

-50

-44

-45

-55

-62

-65

-60

-54

-53

-34

-44

-49

-47

-47

-60

-59

-57

-65

-54

-59

-63

-57

-55

-50

Lomita-1 Wilmington-1 Carson-1 Long Beach-2 Long Beach-1 Cerritos-1 Wilmington-2 Lakewood-1

Hawthorne-1 Willowbrook-1 South Gate-1 Downey-1 La Mirada-1 Whittier-1 Gardena-1 Santa Fe Springs-1

Inglewood-1 Los Angeles-1 Huntington Park-1 Commerce-1 Pico Rivera-1 Pico Rivera-2 Inglewood-2 Rio Hondo-1

-26A2-7 -32F1-5 -9H9-12 -1N3-8 -5H5-10 -5P9-14

-17G3-8 -13J5-8 -8J1-4 -6B4-8 -9J1-6 -9D1-5 -26E2-6 -2K4-8

-28M3-7 -26N3-6 -17F1-5 -22C1-5 -7J1-6 -26D9-14 -18C4-7 -25G3-8

-28A3-7 -25G1-6

Upper Lower Pico unit

Name on top is 

common name

Boundary between

Upper and Lower

aquifer systems,

where present

Boundary between

Lower aquifer systems 

and Pico unit, where

present

Well perforation

No data

Aquifer systems

grouping for geochemical analysis

EXPLANATION

USGS mulitple-well

monitoring site and

abbreviated number –

Figure 15.—Continued.
50 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Seawater

Colorado

River water

State Project

water

Selected wells in the Montebello 

Forebay (Schroeder and others, 1997)

Imported water

Global meteoric water line

(Craig, 1961)

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

-13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1

DELTA OXYGEN-18 (18

O), IN PER MIL

DELTA DEUTERIUM (D), IN PER MIL

Wells in the Central Basin

Wells in the West Coast Basin

A

Figure 16. Delta deuterium as a function of delta oxygen-18 in ground water sampled in the study area (A), in the Central Basin (B), in the West Coast Basin 

(C), Los Angeles County, California.
Geochemical Analysis 51

-60

-50

-40

-30

DELTA DEUTERIUM (

D), IN PER MIL

B

-90

-80

-70

-11 -10 -9 -8 -7 -6 -5 -4

DELTA OXYGEN-18 (18O) , IN PER MIL

Wells perforated in the Pico unit

Wells perforated in the Lower

 aquifer systems

Wells perforated in the Upper

 aquifer aystems

Global meteoric water line

(Craig, 1961)

Lighter Central

Basin water

1E2

9J3

25G5 26D11

Production wells within 500 feet of Montebello 

Forebay spreading grounds

(Schroeder and others, 1997)

(B) Native Montebello Forebay water

D  55 per mil

(A) Native Los Angeles Forebay water

D  47 per mil

Heavier Central

Basin water

Central Basin

Figure 16.—Continued.
52 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California DELTA DEUTERIUM (D), IN PER MIL

Global meteoric water line

(Craig, 1961)

West Coast Basin water –

mixed with imported or sea water,

delta deuterium offset greater

than 3 per mil

Typical West Coast Basin water

D  47 per mil

Lighter West Coast

Basin water

Heavier West Coast

Basin water

26A6

26A7

27E2

32F5

28M7

-9D1

-90

-80

-70

-60

-50

-40

-30

-11 -10 -9 -8 -7 -6 -5 -4

DELTA OXYGEN-18 (18

O), IN PER MIL

C

Wells perforated in the Pico unit

Wells perforated in the Lower

 aquifer systems

Wells perforated in the Upper

 aquifer systems

West Coast Basin

Figure 16.—Continued.
Geochemical Analysis 53

One group of samples plots above the meteoric 

water line at about -47 per mil δD (fig. 16B) and is 

associated with wells located within the Los Angeles 

Forebay (2S/13W-17F3–4, -22C1, and -22C2), near the 

Los Angeles Forebay (2S/14W-23H3, 2S/13W-32R13, 

3S/12W-6B4, and -6B8, and 2S/12W-7J2), and 

downgradient of the Los Angeles Forebay 

(3S/13W-8J2, -21R3, and -26C1, 3S/12W-30K2, 

2S/14W-26N5,). Water in this group originates as 

precipitation falling on the lower lying hills of the San 

Fernando Valley (feeding the Los Angeles River) and 

is a source of recharge and underflow to the Los 

Angeles Forebay. This water occurs throughout the 

western half of the Central Basin, primarily in the 

Lower aquifer systems; extensiveness in the Upper 

aquifer systems is uncertain.

A second group of samples plots above the 

meteoric water line at about -55 per mil δD (fig. 16B) 

and is associated with numerous wells perforated in the 

Lower aquifer systems throughout the distal part of the 

Central Basin Pressure Area (4S/12W-28H1, -25G2, 

-5H6, and -10H1, 4S/11W-5P10, and 3S/11W-26E3) 

and in a few deep wells near the Montebello Forebay 

(2S/11W-18C5, 2S/12W-26D9, and 3S/12W-9J1). 

Water in this group originates as precipitation falling 

on the relatively higher San Gabriel Mountains and is a 

source of recharge and underflow to the Montebello 

Forebay. This water also is present in some wells 

perforated in the Upper aquifer systems in the distal 

part of the Central Basin Pressure Area (4S/13W-1N3, 

4S/12W-5H9, and 4S/11W-5P13). 

In addition to these two main groups, other sets 

of samples in the Central Basin have an isotopic 

composition that plots above (or near) the meteoric 

water line. Isotopically heavy water (from -36 to 

-43 per mil δD) present in wells 4S/13W-1N7–8 (near 

the Dominguez Gap area) and 2S/12W-7J6 (near 

Commerce) (fig. 15) is attributed to local precipitation 

in the coastal plain and surrounding hills. In general, 

this water seems to be limited to shallow portions of 

the Central Basin, although it is present at all 

monitored depths at the Whittier-1 monitoring site 

(3S/11W-2K4–8; fig. 16B). Isotopically light water 

(less than -60 per mil δD) in a few wells perforated in 

the Lower aquifer systems or Pico unit (2S/14W-26N4, 

2S/11W-18C4, 4S/13W-1N4, and 4S/12W–5H5) is 

depleted by -6 to -11 per mil δD and chemically distinct 

from samples collected from overlying wells at the 

same location. These isotopic values are consistent 

with recharge during cooler conditions during the late 

Pleistocene (Clark and Fritz, 1997). Water that plots 

between the Los Angeles and the Montebello forebay 

groups (fig. 16B) may result from a combination of 

recharge from these sources (for example, wells 

4S/13W-1N5–6 and 4S/12W-6K4; between the 

Montebello Forebay and Whittier Area (wells 

3S/11W-9D2 and -9D4).

Most samples in the Central Basin with isotopic 

compositions that plot below the meteoric water line 

and contain less than -50 per mil δD are associated with 

wells proximal to the Montebello Forebay. Within the 

Montebello Forebay, values for the Upper and Lower 

aquifer systems cluster at about -55 and -61 per mil δD, 

respectively (fig 15). Many wells in the Lower aquifer 

systems have an isotopic composition (fig. 16A) that is 

nearly identical to that of several wells within 500 ft of 

the Montebello Forebay spreading grounds (Schroeder 

and others, 1997).

In the study area, the extent to which a sample is 

offset below the meteoric water line often reflects the 

degree of mixing of native and artificially recharged 

water. For example, the distinct isotopic composition 

of water from wells 3S/12W-9J3, 4S/11W-25G5, and 

2S/12W-26D11 in the Central Basin (fig. 8) can be 

explained by substantial mixing with an imported 

source of water. This mixing is evident in water from 

well 5S/12W-1E2 because only imported Colorado 

River water is injected at the nearby Alamitos Gap 

Barrier Project. Recharge to this well (assuming a twocomponent mixture) is estimated to be approximately 

25 percent native Central Basin water and 75 percent 

imported Colorado River water.

West Coast Basin

In the West Coast Basin, δD values for water in 

sampled wells ranged from -34 to -76 per mil. Many 

samples from the Lower aquifer systems (for example, 

4S/13W-9H11 and 3S/14W-13J7 and -17G5) and a few 

from the Upper aquifer systems (4S/13W-9H12 and 

3S/14W-17G7) plot above the meteoric water line at 

about -47 per mil δD (shaded area, fig 16C). This range 

of δD and δ18O is typical of most native ground water 

in the West Coast Basin. The similarity in isotopic 

composition between this group and water in the Los 

Angeles Forebay suggests they share the same source 

of recharge. 
54 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Relatively heavy water, which plots near the 

meteoric water line (-39 to -43 per mil δD; fig. 16C), is 

present in selected wells located near the coast 

(2S/14W-31H1), close to the Newport-Inglewood 

Uplift near Baldwin Hills (3S/14W-13J8 and 

2S/14W-28M5–7), and near Palos Verdes Hills 

(4S/14Q-26A2–3, and -26A6) (fig. 15). Recharge of 

precipitation in the coastal plain and surrounding hills 

is the likely source of this isotopically heavy water. 

δD values as heavy as -32 per mil have been measured 

in shallow ground water at a monitoring site on the 

Palos Verdes Hills (T. Johnson, Water Replenishment 

District of Southern California, written commun., 

1999). 

Another source of isotopically heavy water in the 

basin is seawater (0 per mil 6D). The heaviest water 

sampled in the West Coast Basin was in well 

4S/14W-9D1 (about -34 per mil δD). Given the high 

chloride concentration (6,800 mg/L), an isotopic 

composition depleted by more than 3 per mil δD below 

the meteoric water line, and proximity to the coast, 

seawater appears to be a significant source (about 

30 percent) of water to this well.

Injection of imported water along the West Coast 

Basin and Dominguez Gap Barrier Project is an 

important source of recharge to the West Coast Basin. 

The effect of this recharge is evident in the isotopic 

composition of water from wells 4S/13W-27E2, -

28A6, and -28A7, 2S/14W-28M7 and 4S/13W-32F5. 

Mixing of imported and native West Coast Basin water 

yields very light water that plots below the meteoric 

water line fig. 16C). For example, deuterium measured 

in water from well 4S/13W-28A6 (-76 per mil δD) 

suggests a source of recharge composed of at least 

60 percent imported water.

Relatively light water, which plots above the 

meteoric water line (-48 to -60 per mil δD; fig. 16C), 

indicates another distinct source of recharge in part of 

the West Coast Basin. At least two explanations are 

possible. First, some of this water may have recharged 

under cooler climatic conditions in the Los Angeles 

Forebay. For example, water from two wells 

perforating the Pico unit (3S/14W-17G3 and 

2S/14W-28M3) is chemically distinct and is 

isotopically light relative to overlying water commonly 

found in the Lower aquifer systems (fig. 16C). This 

range (about -51 per mil δD) and pattern also is evident 

in water from a few deep wells within the Lower 

Aquifer systems (3S/14W-13J5 and -17G4 and 

4S/14W-2N1) (figs. 8, 15). Second, some of this water 

may have recharged through the Montebello Forebay. 

The isotopic composition of water from wells 

4S/13W-32F1–2 (relative to overlying water; fig. 

16C)) is too light to be explained by climate change 

alone and, moreover, is identical to the composition of 

natural recharge originating from the Montebello 

Forebay (fig. 16B). Movement of water from the 

Central Basin through the Dominguez Gap to these 

wells is supported by isotopically light water from 

upgradient well 4S/13W-1N4 (-61 per mil δD) (fig. 

15). It appears that this water may be limited to deep 

parts of the Lower aquifer systems downgradient from 

the Dominguez Gap.

Tritium

Radioisotopes, such as tritium, can be used to 

estimate the age of water in the ground. To distinguish 

water that was recharged relatively recently from older 

water, samples were analyzed for tritium content. 

Tritium is a naturally occurring unstable isotope of 

hydrogen that decays by beta-particle emission into 

helium-3 (half-life of 12.4 years). Because tritium is 

part of the water molecule and is affected only by 

radioactive decay, it serves as a natural tracer for 

identifying (that is, age dating) recently recharged 

waters (Michel, 1989). Tritium is present—in varying 

concentrations—in seawater, precipitation, surface 

water, and recycled wastewater. In this investigation, 

tritium values are presented as absolute concentrations 

in tritium units (TU); one TU is equivalent to a 3H/1H 

ratio of 10-18, or an equal activity of 3.19 picoCuries 

per liter of pure water.
Geochemical Analysis 55

Prior to 1952, the tritium concentration in 

precipitation in coastal southern California was about 

2 TU (Izbicki, 1996). Assuming that water recharging 

the Los Angeles coastal basin prior to 1952 had a 

tritium concentration of 2 TU or less, the tritium in that 

same ground water would have decayed to a 

concentration less than 0.1 TU (less than measurable in 

this study) by 2000. Beginning in 1952, significant 

quantities of tritium were released into the atmosphere 

from the testing of hydrogen bombs, reaching a 

maximum in 1963 (fig. 17). Owing to enrichment in 

water vapor across the continental land mass, the 

tritium concentration in precipitation for the Colorado 

River Basin—water that was subsequently imported 

for spreading and injection—is higher than in 

precipitation originating in coastal southern California 

(Michel, 1989). Also, because of the time required to 

transport Colorado River water, the concentration of 

tritium entering the ground-water systems lags the 

values shown in figure 17 (Michel and Schroeder, 

1994).

Tritium values in water from wells sampled as 

part of this study range from less than measurable to 

31 TU, and are categorized in figure 18. Water with 

very low, or less than measurable, tritium content is 

interpreted as “older” water recharged prior to 1952. 

Water with tritium content greater than 1.0 TU is 

interpreted as “recent” water recharged after 1952. 

Water with relatively high tritium content (greater than 

8 TU) has a significant portion of recharge that 

occurred around the peak period of weapons testing 

(fig. 17). Water with moderate tritium content (1.0 to 

8 TU) is interpreted as recent but not necessarily 

attributable to recharge during any specific period after 

1952. Interpreting tritium analyses is complicated by 

the potential mixing of older and younger water, by the 

potential leakage of younger water into deep wells 

through well bores (Mazor, 1991; Izbicki, 1996), and 

by values that could be attributed to either side of the 

1963 peak (fig. 17). 

Central Basin

In the Central Basin, tritium values commonly 

ranged from less than measurable to as high as 31 TU. 

Recent water occurs extensively in the Upper and 

Lower aquifer systems within the Montebello Forebay 

and for several miles downgradient in the surrounding 

Central Basin Pressure Area near wells 2S/12W-7J5, 

3S/13W-13F4, -3S/12W-14F1, and -25C1 (figs. 8, 18). 

Recent water also is present in wells near the Alamitos 

Gap Barrier Project (4S/12W-1E2) and along Los 

Angeles River near the Dominguez Gap 

(4S/13W-1N78). The shaded area in figure 18 shows 

the approximate extent of recent water in the Lower 

aquifer systems.

Significant concentrations of tritium (greater 

than 8 TU) occur within the Montebello Forebay, but 

concentrations were generally highest in wells 

downgradient in the Central Basin Pressure Area. Near 

the spreading grounds along the San Gabriel River, 

abundant tritium is present in water at all monitored 

zones (2S/12W-25G3–8; Pico Rivera-2). Near the 

South Gate-1 monitoring site, water containing 

abundant tritium extends to a depth 1,340 ft below land 

surface (3S/12W-6B5; 17 TU). These data, which are 

consistent with stable isotope, chemical, and 

temperature data, show recently recharged water is 

present in the Lower aquifer system. However, tritium 

values at a few locations in or near the Montebello 

Forebay (2S/12W-26D9 and 3S/12W-9J1 and -6B4) 

suggest that the age of water in other deep portions of 

the Lower aquifer systems (as well as the Pico unit) 

exceeds 50 years.

The highest tritium concentration (31 TU) was 

observed in water from well 3S/12W-9J3 (fig. 18), 

possibly corresponding to water recharged near the 

peak period of weapons testing. The maximum tritium 

concentration (decay-corrected to 1996, when the 

sample was collected) in water recharged during this 

period is estimated to be 110 TU; this, however, does 

not account for dispersion within the ground-water 

system. Efforts to obtain a more refined estimate of 

age, through the coupled measurement of tritium and 

helium-3, suggest that most water to this well was 

recharged during 1968 (R. Anders, U.S. Geological 

Survey, written commun., 2001). 
56 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

0

100

200

300

400

500

600

700

1950 1960 1970 1980 1990 2000

YEAR

TRITIUM CONCENTRATION, IN TRITIUM UNITS 

Decay-corrected to the 

 year 2000

Estimated tritium 

concentration

Figure 17. Estimated tritium activities in precipitation, Los Angeles County, California (from Michel, 

1989).
Geochemical Analysis 57

THIS PAGE INTENTIONALLY LEFT BLANK
58 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Gabriel

San

Rio

Hondo

River

Los

River

Angeles

Gabriel

River

San

Rio

Hondo

Los

River

Angeles

Ballona Creek

R15W R14W R13W R12W R11W

T5S T4S T3S T2S T1S

50'

33° 45'

55'

34° 05'

34° 00'

West 

Coast

Basin

Barrier

Project

Dominguez Gap Barrier

Project

Alamitos Gap

Barrier Project

.8, <.1

<.1

1.7

<.1 0.6

.2

1.7

.2

<.1

11

22

7.2

.9, 4.4 .9

.9

1-8 TU

Greater than

 8 TU

20

12

<.1

<.1

<.1

<.1

<.1

<.1

<.1

17

22

<.1

<.1

<.1

23

7.2

9.7

4.7

<.1

24

12

17

Less than 1 TU

5H5-10 1N3-8

8J1-4

26A2-7 28A3-7

32F1-5

9H9-12

9J1-6 9D1-5

26D9-14

25G3-8

26E2-6

5P9-14

25G1-6

2K4-8

7J1-6

22C1-5

6B4-8

17F1-5

13J5-8

28M3-7 26N3-6

17G3-8

18C4-7

USGS multiple-well monitoring site and number – Dashed line indicates

sites sampled for tritium (see facing page) Color Range of values

Production well and number – Wells with perforations located in the:

0 5 MILES

0 5 KILOMETERS

EXPLANATION

San Gabriel Valley

Pacific Ocean

Santa

Monica

Bay

San Pedro Bay

18° 25' 20' 05' 15' 10' 118° 00'

32F1-5

Repetto Hills

Elysian

Hills

Merced Hills

Palos Verdes Hills

Puente Hills

Santa Monica Mountains

Unconsolidated deposits

Consolidated deposits

Spreading grounds

Seawater barrier project

West Coast Basin

Central Basin

Hollywood Basin

Santa Monica

Basin

Montebello

Forebay

Los Angeles

Forebay

Tritium units – (TU)

Whittier Area

Whittier

Narrows

Los Angeles

Narrows

Dominguez Gap

Other well and number – Wells with perforations located in the:

Upper aquifer systems Lower aquifer systems

Upper aquifer systems Lower aquifer systems

Model subareas

Model boundary

Approximate extent of recent water

in the lower aquifer systems ( >1 TU)

Dashed where uncertain

Figure 18. Tritium concentration in ground water sampled in the study area, Los Angeles County, California. Blue areas show approximate extent of recent 

water (greater than 1TU) in the Lower aquifer systems; dashed where uncertain. 
Geochemical Analysis 59

A3

A4

A6

A7

H12

N3 H5

G1

P9

P10

P11

P12

P13

P14

G2

G3

G4

G5

G6

H6

H7

H8

H9

H10

N4

N5

N6

N7

N8

H11

H10

H9

A7

A6

A5

A4

A3

A2

A5

F1

F2

F4

F5

F3

M3

M4

N6

N5

N4

N3

F1

F2

C1

J1

D9

C4

G3

G4

G5

G6

G7

G8

C5

C6

C7

D10

D11

D12

D13

D14

J2

J3

J4

J5

J6

C2

C3

C4

C5

F3

F4

F5

M6

M7

M5

G3 J5

J1

B4

B5

B6

B7

B8

J6

J5

J4

J3

J2

J1

D1

D2

E2

E3

E4

K4

K5

K8

K6

K7

E5

E6

D3

D4

D5

J2

J3

J4

J6

J7

J8

G4

G5

G6

G7

G8

<.1

<.1

19

12

.1

3.8

5.0

<.1

<.1

<.1

<.1

<.1

<.1

.1

1.0

<.1

<.1

1.4

17 --

.2

.4

.3

.5

3.1

<.1

2.0

<.1

.5

<.1

<.1

<.1

.3

26

.1

<.1

<.1

<.1

<.1

<.1

<.1

<.1

<.1

<.1

--

--

.1 <.1

<.1

.1

<.1

<.1

<.1

<.1

<.1

<.1

<.1

.4

<.1

--

.1

5.6

31

18

5.0

16

<.1

17

25

14

<.1

1.0

.1

<.1

<.1

<.1

.1

.3

.3

18

1.0

<.1

<.1

<.1

<.1

<.1

--

.3

1.6

--

.1

.1

.2

<.1

<.1

<.1

<.1

<.1

<.1

--

<.1

19

2.4

.2

<.1

.1

18

13

8.1

8.1

7.2

--

.6

1.3

<.1

<.1

15

12

4.4

<.1

8.4

17

18

8.4

9.1

8.4

1.7

.9

 1-8 TU

Greater than

 8 TU

17

Less than 1 TU

Tritium units – (TU)

Color Range of values

Lomita-1 Wilmington-1 Carson-1 Long Beach-2 Long Beach-1 Cerritos-1 Wilmington-2 Lakewood-1

Hawthorne-1 Willowbrook-1 South Gate-1 Downey-1 La Mirada-1 Whittier-1 Gardena-1 Santa Fe Springs-1

Inglewood-1 Los Angeles-1Huntington Park-1 Commerce-1 Pico Rivera-1 Pico Rivera-2 Inglewood-2 Rio Hondo-1

-26A2-7 -32F1-5 -9H9-12 -1N3-8 -5H5-10 -5P9-14

-17G3-8 -13J5-8 -8J1-4 -6B4-8 -9J1-6 -9D1-5 -26E2-6 -2K4-8

-28M3-7 -26N3-6 -17F1-5 -22C1-5 -7J1-6 -26D9-14 -18C4-7 -25G3-8

-28A3-7 -25G1-6

Name on top is 

common name

Boundary between

Upper and Lower

aquifer systems,

where present

Boundary between

Lower aquifer systems 

and Pico unit, where

present

Well perforation

No data

Aquifer systems grouping

for geochemical analysis

EXPLANATION

USGS mulitple-well

monitoring site and

abbreviated number –

Upper Lower Pico unit

< Less than

Figure 18.—Continued.
60 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Tritium values indicate that water from wells in 

the Los Angeles Forebay and surrounding Central 

Basin Pressure Area is older water. In sharp contrast to 

the Montebello Forebay, only one well in the Los 

Angeles Forebay (2S/13W-22C3), and none of the 

wells downgradient to the west (2S/14W-10Q2), to the 

south (3S/13W-8J3), or along the NIU (3S/13W-21R3) 

contains recent water (greater than 1 TU) (fig. 18). In 

the southeast part of the Central Basin Pressure Area, 

older water is typically present in both aquifer systems. 

Less than measurable tritium in water from wells 

3S/12W-30K2, 4S/12W-5H7 and -10H1, 

4S/11W-5P11, and 3S/11W-9D2 approximates a 

boundary beyond which recent water is absent. An 

exception is made for abundant tritium observed in 

water from wells 5S/12W-1E2 and 4S/12W-25G5 (11 

and 26 TU, respectively). The source of this water 

(based on δD values) is attributed to injection at the 

Alamitos Gap Barrier Project. 

West Coast Basin

In the West Coast Basin, tritium values ranged 

from less than measurable to 22 TU (fig. 18). Most 

wells, especially those in the Lower aquifer systems, 

contain water with low or less than measurable tritium 

concentrations. For example, low tritium values 

highlight the predominance of older water along the 

interior of the basin (2S/14W-28M5, 3S/14W-13J7, 

4S/13W-9H11, -15A11, and -17D2) (fig. 18). Older 

water also is present in many deeper wells 

(3S/14W-17G6 and 4S/13W-32F3 and -28A4) along 

the coast, which suggests that the Lower aquifer 

systems do not contain significant recharge from the 

barrier projects at these locations. 

Recent water in the West Coast Basin is 

generally limited to areas along the coast and to the 

Upper aquifer systems (figs. 8, 18). Near the coast, 

water in the Lower aquifer systems from well 

4S/14W-9D1 may contain a small fraction of recently 

intruded seawater (1.7 TU). Farther inland, water from 

the West Coast Basin Barrier Project may be reaching 

well 4S/13W-1N2, along with a plume of saline water. 

The highest tritium value observed in the West Coast 

Basin (22 TU) was in water from well 4S/13W-27E2, 

and is attributed to injection of imported water at the 

Dominguez Gap Barrier Project. High tritium (greater 

than 8 TU) also is associated with other wells located 

near the barrier projects (3S/14W-17G8 and 

4S/13W-28A7 and -32F5). Near the NIU, moderate 

tritium values in relatively shallow wells 

(2S/14W-28M7 and 3S/14W-13J8) may reflect recent 

recharge from local precipitation.

Carbon-14

Samples from selected wells were analyzed for 

carbon-14 to further distinguish the relative age of 

older water in the basin. Carbon-14 is a naturally 

occurring unstable isotope of carbon with a half-life of 

5,730 years that can be used to estimate ground-water 

age (since time of recharge) up to about 20,000 years 

(Gat and Gonfiantini, 1981). Carbon-14 data are 

reported as percent modern carbon (pmc) by 

comparing carbon-14 activities with the specific 

activity of National Bureau of Standards oxalic acid; 

12.88 disintegrations per minute per gram of carbon in 

the year 1950 equals 100 percent modern carbon 

(Izbicki and others, 1998). Like tritium, significant 

quantities of carbon-14 were released into the 

atmosphere from the testing of hydrogen bombs. As a 

result, very recent water may contain carbon-14 in 

excess of 100 pmc. Unlike tritium, carbon-14 is not 

part of the water molecule; rather it is introduced into 

the ground-water system through plant respiration, 

decay of organic matter in soils, and dissolution of 

minerals and, as such, is subject to reactions that occur 

between dissolved constituents and the aquifer matrix 

(Fontes, 1985). 

Samples for which carbon-14 activity was 

determined ranged from 1 to 123 pmc (fig. 19); most 

are from wells perforated in the Lower aquifer systems. 

Ground-water ages (corresponding to measured 

carbon-14 activity) discussed in this report are apparent 

ages (recharge, in years before present) and relative to 

water in well 2S/11W-18C5, which contains 90 pmc. 

These estimates are not corrected for reactions within 

the aquifer, and therefore they may not reflect the true 

age of the water. In other words, the apparent age given 

by the carbon-14 value represents the maximum age 

possible for the ground water. Based on work in an 

adjacent coastal basin (Izbicki, 1996), use of 

uncorrected carbon-14 values may overestimate the 

groundwater age by 20 to 50 percent. 
Geochemical Analysis 61

THIS PAGE INTENTIONALLY LEFT BLANK
62 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Gabriel

San

Rio Hondo

River

Los

River

Angeles

Gabriel River San

Rio

Hondo

Los

River

Angeles

Ballona Creek

R15W R14W R13W R12W R11W

West 

Coast

Basin

Barrier

Project

Dominguez Gap Barrier

Project

Alamitos Gap

Barrier Project

77

90

10, 39

70

38

38, 40

Less than 40

40 - 80

Greater than 80

66 66

77

5H5-10 1N3-8

8J1-4

28A3-7

26A2-7

32F1-5

9H9-12

9J1-6

9D1-5

26D9-14

25G3-8

26E2-6

5P9-14

25G1-6

2K4-8

7J1-6

22C1-5

6B4-8

17F1-5

13J5-8

28M3-7

26N3-6

17G3-8

18C4-7

USGS multiple-well monitoring site and number – Dashed line 

indicates sites sampled for carbon-14 (see facing page)

Production well and number – Wells with perforations located in the:

0 5 MILES

0 5 KILOMETERS

EXPLANATION

San Gabriel Valley

Pacific Ocean

Santa

Monica

Bay

San Pedro Bay

18° 25' 20' 05' 15' 10' 118° 00'

32F1-5

Repetto Hills

Elysia

H

n

ills

Merced Hills

Puente Hills

Santa Monica Mountains

West Coast Basin

Central Basin

Hollywood Basin

Santa Monica

Basin

Montebello

Forebay

Los Angeles

Forebay

Carbon-14 activity – 

Percent modern carbon

Color Range of values

Whittier Area

T5S T4S T3S T2S T1S

50'

33° 45'

55'

34° 05'

34° 00'

Other well and number – Wells with perforations located in the:

Lower aquifer systems

Upper aquifer systems Lower aquifer systems

Whittier

Narrows

Los Angeles

Narrows

Dominguez Gap

Palos Verdes Hills

Unconsolidated deposits

Consolidated deposits

Spreading grounds

Seawater barrier project

Model subareas

Model boundary

Figure 19. Carbon-14 activities in sampled ground water in the study area, Los Angeles County, California.
Geochemical Analysis 63

A3

A4

A6

A7

H12

N3 H5

G1

P9

P10

P11

P12

P13

P14

G2

G3

G4

G5

G6

H6

H7

H8

H9

H10

N4

N5

N6

N7

N8

H11

H10

H9

A7

A6

A5

A4

A3

A2

A5

F1

F2

F4

F5

F3

M3

M4

N6

N5

N4

N3

F1

F2

C1

J1

D9

C4

G3

G4

G5

G6

G7

G8

C5

C6

C7

D10

D11

D12

D13

D14

J2

J3

J4

J5

J6

C2

C3

C4

C5

F3

F4

F5

M6

M7

M5

G3 J5

J1

B4

B5

B6

B7

B8

J6

J5

J4

J3

J2

J1

D1

D2

E2

E3

E4

K4

K5

K8

K6

K7

E5

E6

D3

D4

D5

J2

J3

J4

J6

J7

J8

G4

G5

G6

G7

G8

30

44

--

--

--

--

--

--

22

4

1

56

44

28

--

3

5

--

-- --

--

--

--

--

--

14

--

59

61

54

72

8

--

61

53

24

30

31

--

59

57

34

46

56

-- -- --

--

--

15

15

15

--

22

53

20

--

--

--

--

74

86

123

--

--

--

48

94

--

--

--

--

--

--

68

16

--

65

9

--

--

16

10

8

3

--

--

--

--

--

--

--

--

--

--

53

--

--

--

--

28

35

83

--

96

--

--

--

--

--

84

84

82

76

57

53

--

--

90

2

93

111

--

--

--

--

90

Less than 40

Carbon-14 activity – 

Percent modern carbon

Color Range of values

2

 40 - 80

Greater than

 80

57

Upper Lower Pico unit

Name on top is 

common name

Boundary between

Upper and Lower

aquifer systems,

where present

Boundary between

Lower aquifer 

systems and Pico unit, 

where present

Well perforation

No data

Aquifer systems 

grouping for 

geochemical analysis

EXPLANATION

USGS mulitple-well

monitoring site and

abbreviated number –

Lomita-1 Wilmington-1 Carson-1 Long Beach-2 Long Beach-1 Cerritos-1 Wilmington-2 Lakewood-1

Hawthorne-1 Willowbrook-1 South Gate-1 Downey-1 La Mirada-1 Whittier-1 Gardena-1 Santa Fe Springs-1

Inglewood-1 Los Angeles-1 Huntington Park-1 Commerce-1 Pico Rivera-1 Pico Rivera-2 Inglewood-2 Rio Hondo-1

-26A2-7 -32F1-5 -9H9-12 -1N3-8 -5H5-10 -5P9-14

-17G3-8 -13J5-8 -8J1-4 -6B4-8 -9J1-6 -9D1-5 -26E2-6 -2K4-8

-28M3-7 -26N3-6 -17F1-5 -22C1-5 -7J1-6 -26D9-14 -18C4-7 -25G3-8

-28A3-7 -25G1-6

Figure 19.—Continued.
64 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

The apparent ages corresponding to carbon-14 

activities, grouped according to tritium content, for 

selected wells in the study area are shown in table 2. 

Water containing less than 1 TU contains carbon-14 

with an activity of 1 to 84 pmc. This is predominantly 

older water with an apparent age between several 

thousand to several hundred years before present. 

Uncorrected carbon-14 data from four wells 

perforating the Pico unit (1 to 7 pmc) suggest that 

recharge is on the order of 20,000 years before present. 

Water containing more than 1 TU and carbon-14 

values exceeding 89 pmc is recent water (table 2). 

Water containing more than 1 TU and carbon-14 

values less than 90 pmc may result from a mixture of 

recent and older water, or significant dissolution of 

aquifer material. In both circumstances, an apparent 

age cannot be accurately assigned. 

Central Basin

Carbon-14 values in the Central Basin ranged 

from 1 to 123 pmc (fig 19). The median value in the 

Lower aquifer systems is 56 pmc. Carbon-14 values are 

high in the forebay areas and generally decrease with 

depth and distance downgradient. In the Montebello 

Forebay area several wells yielded recent water 

(greater than 1 TU) with carbon-14 values greater than 

80 pmc. The highest carbon-14 value in the Central 

Basin was observed in water from 3S/12W-9J3 (123 

pmc; also the highest tritium concentration) and is 

consistent with recent (bomb influenced) water. 

Similarly, carbon-14 values for wells 3S/12W-6B5 and 

2S/12W–25G3–4 (94, 93, and 111 pmc, respectively) 

illustrate the vertical extent of this very recent water. 

However, carbon-14 in water from well 2S/12W-26D9 

(35 pmc) indicates that much older water (about 7,700 

years in table 2) is present in deep portions of the 

Montebello Forebay.

In the Los Angeles Forebay, carbon-14 activity 

is greater than 80 pmc in a few wells (2S/13W-17F2, 

and -22C1–2) perforated in the Lower aquifer systems. 

This is older water (less than 1 TU) with an apparent 

age of about 600 to 800 years (table 2). The carbon-14 

value for water from another well, 2S/13W-17F1 

(53 pmc), in the Los Angeles Forebay, indicates a 

substantial increase in apparent age (4,400 years) with 

depth in the Lower aquifer systems.

Downgradient wells from the Los Angeles 

Forebay in the Central Basin Pressure Area 

(3S/13W-8J2 and -21R3, 3S/12W-30K2, and 

2S/13W-31C3) yielded water with carbon-14 values 

(66 to 70 pmc) corresponding to an apparent age range 

of about 2,100 to 2,600 years (fig. 19; table 2). Much 

farther downgradient, very old water (about 

20,000 years) is present in wells in the Lower aquifer 

systems (4S/13W-1N4 and 4S/12W-5H5). Water from 

this part of the basin does not contain any significant 

fraction of recent water (fig. 18) and is considered to be 

representative of native water. 

In the Whittier area, water from the three lower 

wells at the Whittier-1 site (3S/11W-2K4, 5, and 8) has 

the same carbon-14 values (15 pmc), possibly as a 

result of deep circulation to the Lower aquifer systems. 

West Coast Basin

In the West Coast Basin, carbon-14 values 

ranged from 2 to 65 pmc for water in the Lower aquifer 

systems (fig. 19). The median carbon-14 value is 

28 pmc–substantially less than that in the Central 

Basin–and values generally decrease with depth and 

toward the coast. These data are consistent with a long 

travel times for water moving from the forebays, across 

the NIU, to the coast. For example, carbon-14 values 

from deeper wells in the Lower aquifer systems at the 

USGS Gardena-1 (9 and 65 pmc) monitoring site are 

similar to values at USGS Willowbrook-1 (16 and 

68 pmc) (fig. 19). Furthermore, carbon-14 and stable 

isotope (fig. 15) data at these two sites do not show that 

the Newport-Inglewood Uplift greatly impedes flow 

between the basins in this area. In contrast, chemistry 

and stable-isotope data from the USGS Inglewood-1 

and USGS Inglewood-2 sites are very different from 

each other, indicating that the NIU acts as a significant 

barrier between these locations. 
Geochemical Analysis 65

Table 2. Carbon-14 and apparent-age for selected wells sampled, Los Angeles County, California—Continued

Measured carbon-14 

(pmc)

Apparent age

(years before present) Basin Aquifer System 

or unit State well No.

Water containing less than 1 tritium unit

1 37,000 C Pico 4S/13W-1N3

2 33,000 C Pico 2S/11W-18C4

3 29,000 W LSP 4S/13W-32F1

3 29,000 W Pico 3S/14W-17G3

4 25,000 C LSP 4S/13W-1N4

5 24,000 W USP 4S/13W-32F2

7 21,000 C Pico 2S/12W-7J1

8 20,000 W, C LSP 3S/14W-17G4, 4S/12W-5H5

9 19,000 W LSP 3S/14W-13J5

10 18,000 W USP, LSP 3S/14W-17G5, 4S/14W-2N1

14 15,000 W USP 4S/13W-32F3

15 15,000 C USP 3S/11W-2K4, -2K5, -2K8

16 14,000 W USP 3S/14W-17G6

16 14,000 C LSP 3S/13W-8J1

20 12,000 C LSP 3S/11W-26E2

22 12,000 C USP 3S/11W-26E4, 4S/13W-1N5

24 11,000 C USP 4S/12W-25G3

28 9,800 W USP 4S/13W-9H9

28 9,500 C LSP 2S/12W-7J2

30 9,200 W LSP 4S/13W-28A3

30 9,100 C LSP 4S/12W-25G2

31 8,800 C LSP 4S/12W-25G1

34 8,000 C USP 4S/11W-5P11

35 7,700 C LSP 2S/12W-26D9

38 7,200 W USP 4S/14W-2N3

39 7,000 W USP 4S/14W-2N2

Table 2. Carbon-14 and apparent-age for selected wells sampled, Los Angeles County, California

[Carbon-14: measured activity. Apparent age: the maximum in years before present since recharged. Assumes an initial activity of 90 percent modern carbon 

during recharge—not corrected for reactions within the aquifer matrix. Basin: C, Central; W, West Coast. Aquifer or unit: Pico, Pico unit; LSP, Lower San 

Pedro; USP, Upper San Pedro; Lake, Lakewood] 
66 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

1Mixture of recent (less than 50 years before present) and older water.

44 6,000 W USP 4S/13W-9H10

44 5,800 W LSP 4S/13W-28A4

46 5,500 C LSP 4S/11W-5P10

48 5,100 C LSP 3S/12W-6B4

53 4,400 C LSP 2S/13W-17F1, 3S/11W-26E3

53 4,400 W LSP 2S/14W-28M5

53 4,400 C USP 4S/12W-25G4

54 4,200 C USP 4S/12W-5H6

56 3,900 W USP 4S/13W-9H11

56 3,900 C LSP 4S/11W-5P9

57 3,800 C LSP, USP 2S/12W-7J3, 4S/11W-5P12

59 3,500 C Lake 4S/12W-5H8

61 3,200 C USP 4S/12W-5H7

65 2,600 W USP 3S/14W-13J6

66 2,600 C USP 3S/12W-30K2, 3S/13W-21R3

68 2,300 C USP 3S/13W-8J2

70 2,100 C USP 2S/13W-31C3

72 1,800 C Lake 4S/12W-5H9

74 1,600 C USP 3S/12W-9J1

76 1,300 C USP, Lake 2S/13W-7F4, 4S/11W-9P13

77 1,300 C USP 4S/12W-10H1

82 800 C USP 2S/13W-17F2

84 600 C USP 2S/13W-22C1–2

Water containing more than 1 tritium unit

40 Mixture1 W Lake 4S/14W-2N4

61 Mixture1 C USP 4S/12W-25G5

83 Mixture1 C USP 2S/12W-26D10

86 Mixture1 C USP 3S/12W-9J2

90 Recent C LSP 2S/11W-18C5

93 Recent C LSP 2S/12W-25G3

94 Recent C USP 3S/12W-6B5

96 Recent C USP 2S/12W-26D12

111 Recent C USP 2S/12W-25G4

123 Recent C USP 3S/12W-9J3

Table 2. Carbon-14 and apparent-age for selected wells sampled, Los Angeles County, California—Continued

Measured carbon-14 

(pmc)

Apparent age

(years before present) Basin Aquifer System 

or unit State well No.
Geochemical Analysis 67

Water from well 4S/14W-2N3–4 contained 38 

and 40 pmc, respectively, indicating water of 

significant age is present in the Upper aquifer systems 

(table 2). However, water from well 4S/14W-2N4 also 

contained 4.4 TU. This water is a mixture of recent 

water (possibly from injection at the West Coast Basin 

Barrier Project) (fig. 18) and possibly very old ground 

water. Very old water is present in water from wells 

near the coast (3S/14W-17G4 and 4S/13W-32F1; 8 and 

3 pmc, respectively) and corresponds to an apparent 

age on the order of 20,000 years. Water in both of these 

wells has a slight to strong measurable color and odor. 

Integrated Geochemical Analysis of the Regional 

Ground-Water Flow System

To further evaluate movement of water within 

the study area and to better understand changes in the 

ground-water flow system, aspects of the chemistry 

and isotope data are integrated along two cross sections 

of the Los Angeles basin (fig. 20). The section lines 

shown in figure 8 were modified from geohydrologic 

sections (fig. 2) to approximate ground-water 

flowpaths from the forebays prior to development of 

the basin. 

The chemical character of ground water changes 

as it moves downgradient from the forebay as a result 

of water-mineral interactions and mixing within an 

aquifer system. Primary controls on the degree of 

change depend on (1) sources of recharge, (2) mineral 

assemblages derived from weathering and from 

mountains surrounding the study area, and 

(3) residence time of the ground water. Some of the 

processes and water-mineral interactions that affect the 

ground-water chemistry along the section lines shown 

in figure 20 are summarized in table 3. Redox 

processes (not shown) that affect ground-water 

chemistry involve manganese, nitrogen, and molecular 

oxygen.

A geohydrologic section emanating from the 

Montebello Forebay and extending into the Central 

Basin Pressure Area is shown in figure 20A. Relatively 

fresh water is present throughout the section. Tritium 

(greater than or equal to 1 TU) in water, along with 

chemical and isotopic data, shows that artificial 

spreading of water in the Montebello Forebay 

recharges the ground-water system at significant 

depths and distances from the spreading facilities. Data 

indicate that the Upper aquifer systems typically 

contain recent water spanning a range of chemical 

character owing to multiple sources of artificial 

recharge. In the Lower aquifer systems, this water, 

away from the Montebello Forebay, is also shown in 

well 3S/12W–33A7. Although stable-isotope data 

indicate that the bulk of recharge to this well is native 

water originating from the San Gabriel Valley, the 

presence of moderate tritium (7.2 TU) (fig. 18) 

suggests a component of ground water having 

recharged less than 50 years ago. Some of the recent 

water occurring in the Lower aquifer systems—

specifically the Lower San Pedro aquifer system 

(2S/11W-18C5)—may also be related to underflow 

through the Whittier Narrows. 

A geohydrologic section emanating from the Los 

Angeles Forebay and extending across the NIU into the 

West Coast Basin is shown in figure 20B. Recent water 

is yielded by two wells in the Los Angeles Forebay 

(2S/13W-17F5 and -22C4) and a few wells near the 

coast. This reflects the limited recharge in the Los 

Angeles Forebay (in comparison with the Montebello 

Forebay) and the effects of injection at the Dominguez 

Gap Barrier Project. Older water is yielded by deep 

wells of the Los Angeles Forebay, shallow and deep 

wells downgradient along section C’–B', and wells near 

the interior of the West Coast Basin. Carbon-14 data 

show that apparent ground-water ages generally 

increase with depth and distance away from the 

forebay. Furthermore, carbon-14 data show significant 

differences in the relative ages of water within the 

Lower aquifer systems. 
68 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California Tritium (greater than or equal to 1TU) in water – Dashed where approximately located, queried where uncertain

?

?

?

? ?

?

400400800

1,2001,600

FEET

Sea

level

18C4-7

26D9-14

5H5-10 28H1*

33A7*

25C1*

16H1*

28J6*

A' A''

00 5 KILOMETERS

5 MILES

Whittier

Narrows

Montebello Forebay Central Basin Pressure Area

Spreading Grounds

9J1-6

11E1*

212

--

181

8

358

--

484

--

418

--

500

74

211

74

362

2

307

90

577

--

649

--

446

83

450

--

467

96

355

--

341

--

344

86

380

--

482123

529

--

811

--

519

--

206

54

247

61

278

59

610

-- 256

72

280

35

?

?

EXPLANATION

Multiple-well monitoring site – Geologic contact – Dashed

where approximately located,queried where uncertain

Screened

interval

Abbreviated well number Well

casing

Vertical scale greatly exaggerated Datum is sea level

? 26D9

Upper

aquifer

systems

Lower

aquifer

systems

Aquifer system

RecentLakewoodUpper San PedroLower San PedroPico Unit

280

35

Dissolved solids concentration – In milligrams per liter (see figure 10 for number color scheme)Carbon-14 activity – In percent modern carbon (see figure 19 for number color scheme)

* Well projected to section line

-- No data

A

Figure 20. Dissolved-solids concentration, measurable tritium activity, and carbon-14 activity in ground water from wells sampled along geohydrologic sections A’–A’’ (A) and C’–B’ (B), Los Angeles 

County, California.
Geochemical Analysis 69

?

?

?

Tritium (greater than or equal to 1 TU) in water - Dashed where approximately located, queried where uncertain

400400800

Sea

level

1,2001,600

9H9-12

22C1-5

17F1-5*

11R4*

32R13

21R3*

17D2*

00 5 KILOMETERS

5 MILES

C' B' Los Angeles Forebay 

NewportInglewood

Uplift

Central Basin Pressure Area West Coast Basin

31C3*

-22C1

Dominguez

Channel

Dominguez

Gap Barrier

Project

28A3-7

27E2*

358

--

341

84

353

84

466

--

377

--

462

76

641

--

373

82

351

53

658

----

--

345

70

353

--

311

16

319

68

332

--

304

66

206

28

230

44

248

--

490

30

787

44

1,720

--

2,470

--

6,380

--

320

56

574

--

347

--

8J1-4

?

?

?

FEET

Upper

aquifer

systems

Lower

aquifer

systems

Aquifer system

EXPLANATION

Geologic contact – Dashed whereapproximately located,queried where uncertain

Screened

interval

RecentLakewoodUpper San PedroLower San PedroPico Unit

Well

casing

Vertical scale greatly exaggerated Datum is sea level

?

B

341

84

Multiple-well monitoring site – 

Abbreviated well number

Dissolved solids concentration – In milligrams per liter (see figure 10 for number color scheme)Carbon-14 activity – In percent modern carbon (see figure 19 for number color scheme)

* Well projected to section line

-- No data

Figure 20.—Continued.
70 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

To clarify the source and movement of recharge 

waters in the study area, oxygen-18 and deuterium 

were plotted, and then grouped by available tritium 

concentrations. As shown in figure 21, nearly all 

waters that have very low, or less than measurable, 

tritium plot above the meteoric water line. This older 

water in the study area originates, predominantly, from 

the San Fernando Valley (about -47 per mil δD) and the 

San Gabriel Valley (about -55 per mil δD). This water 

is similar to “native fresh waters of good chemical 

quality” described by Piper and Garrett (1953). 

All recent water in figure 21 that has significant 

tritium (greater than 8 TU) plots below the meteoric 

water line. Most points cluster at about –61 per mil δD, 

are chemically distinct, and show the influence of 

artificially recharged water. The extent to which a 

sample is offset below the meteoric water line largely 

reflects the relative proportion of native water that has 

mixed with artificially recharged water. The effect of 

this mixing is evident in water from well 5S/12W-1E2 

since only imported Colorado River water is injected at 

the nearby Alamitos Gap Barrier Project. Assuming 

only a two-component mixture, recharge to this well 

(based on δD values) consists of 25 percent native 

Central Basin water and 75 percent imported Colorado 

River water.

In figure 21, water from a few wells has 

moderate tritium values (1 to 8 TU) and varied isotopic 

composition. Few regional generalizations can be 

drawn from this group, as differences likely reflect a 

combination of local hydrologic factors. For example, 

values for wells 4S/14W-9D1 and 4S/14W-2N4 could 

result from a mixture of seawater, imported water, and 

(or) native water (fig. 8). Values for other wells 

associated with this group may indicate recently 

recharged native water in the Dominguez Gap 

(4S/13W-1N8) and Whittier Narrows (2S/11W-18C5) 

areas.

Table 3. Processes and reactions controlling water quality along geohydrologic sections A’–A” and C’–B’, Los Angeles County, California

Process Reaction Note

1. Sulfate reduction 2CH2O + SO4

-2 → H2S + 2HCO3-2 Requires organic material (generalized as 

CH2O)in aquifer; mediated by sulfatereducing bacteria

2. Cation exchange 2Na+ + Ca–clay → Ca+2 + Na2–clay Exchange of dissolved calcium (or 

magnesium) in water for sodium on clay 

minerals 

3. Calcite precipitation HCO3

-

 + Ca+2 → CaCO3 + H+ Precipitation of minerals that remove ions 

from the water 

4. Evaporite dissolution NaCl(s) → Na+ + ClCaSO4(s) → Ca+2 + SO4

-2

Salts from areas of ground-water discharge, 

lagoons, or semi-perched aquifers

5. Iron cycling Oxidation/reduction, dissolution Iron-hydroxides; iron-silicates; pyrite
Geochemical Analysis 71

-90

-80

-70

-60

-50

-40

-30

-11 -10 -9 -8 -7 -6 -5 -4

DELTA OXYGEN-18, IN PER MIL

DELTA DEUTERIUM, IN PER MIL

Less than 1 TU

Greater than 8 TU

Water containing:

1-8 TU

Global meteoric water line

3S/12W-33A7

2S/11W-18C5

5S/12W-1E2

2S/13W-17F5

4S/14W-2N4

2S/13W-22C4

4S/13W-1N8

4S/14W-9D1

Figure 21. Delta deuterium as a function of delta oxygen-18, grouped by tritium concentration in ground water sampled in the study 

area, Los Angeles County, California.
72 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

DEVELOPMENT OF A GROUND-WATER 

SIMULATION MODEL

A ground-water simulation model was 

developed to synthesize the understanding of the threedimensional geohydrologic system and to serve as a 

tool to evaluate alternative ground-water management 

strategies. The model covers the entire study area, 

including parts offshore. The grid for the model is 

shown in figure 22. The model uses the USGS 

MODFLOW program (McDonald and Harbaugh, 

1988; Harbaugh and Mc Donald, 1996). The uniform 

finite-difference grid consists of 4,480 cells, each 

0.5 mi by 0.5 mi. The model includes separate layers 

for the four main aquifer systems described earlier 

(fig. 3). The extent of layer 1, representing the Recent 

aquifer system, is limited and is based on the extent of 

the Gaspur aquifer. First, a steady-state model was run 

to approximate conditions in water year 1971. A 

30-year transient case (1971–2000) was then simulated 

using yearly stress periods.

Required model inputs include boundary 

conditions, elevation of aquifer-system bases, 

hydraulic conductivities, storage properties of the 

aquifer systems, vertical conductance between aquifer 

systems, conductance across faults, recharge, and 

pumpage. Layer 1 was modeled as unconfined (a Type 

1 layer in MODFLOW) with layer base, specific yield, 

and hydraulic conductivity specified. Layers 2–4 were 

modeled as confined/unconfined (Type 3 layers in 

MODFLOW) with layer top, layer base, confined 

storage coefficient, specific yield, and hydraulic 

conductivity specified. Re-wetting was allowed for 

layers 1 through 3 (layer 4 did not go dry in any of the 

simulations). 

Boundary Conditions

The model-boundary conditions are no-flow 

along the boundary with Tertiary deposits to the north 

and northeast (the Santa Monica Mountains and the 

Elysian, Repetto, Merced, and Puente Hills) and to the 

southwest (the Palos Verdes Hills) (figs. 1, 22). Within 

the model domain, the Baldwin Hills also are modeled 

as no-flow cells. For layer 1 (fig. 22A) no-flow 

boundaries are used to represent the estimated areal 

extent of the Gaspur aquifer. General-head boundaries 

were used at the Los Angeles and Whittier Narrows to 

represent ground-water underflow from San Gabriel 

and San Fernando Valleys. These general-head 

boundaries were applied using average measured water 

levels over the simulation period at wells along these 

boundaries (well 1S/13W-14E3 for the Los Angeles 

Narrows and wells 2S/11W-5L1 and -6G2 for the 

Whittier Narrows; these water levels are quite constant 

over the simulation period) (fig. 23). The general-headboundary conductance specified in MODFLOW for the 

cells at these two boundaries is 0.3 ft2/s. Time-varying 

specified head boundaries were used at the Los 

Angeles−Orange County boundary in the Central Basin 

to represent ground-water underflow to and from the 

Orange County ground-water basin (note, the model 

boundary actually extends from 0.5 to 3 miles into 

Orange County). The specified-head boundaries were 

set on the basis of measured water levels over the 

simulation period at wells 3S/11W-35J3, 4S/11W-4K1, 

-19R1, and 5S/11W-7C1 (fig. 23). Values used for 

these wells are the averages of the annual minimum 

and maximum levels. Water levels at these wells are 

assumed to represent conditions in model layer 3 

(fig. 22C). Comparable water levels for layers 2 and 4 

(layer 1 is not active at this boundary) were estimated 

on the basis of relative heads at the USGS multiplewell monitoring sites La Mirada-1, Cerritos-1, and 

Long Beach-1. The implications of applying this 

boundary condition are discussed and tested later.
Development of a Ground-Water Simulation Model 73

Puente Hills

Santa Monica

Bay

San Pedro

Bay

Whittier

Narrows

Los Angeles

Narrows

Layer 1

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

0 10 MILES

0 10 KILOMETERS

33°

40'

50'

34°

00'

118° 30' 20' 10' 118° 00'

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Repetto Hills

Elysia

H

n

ills

Merced Hills

San

Valley

Gabriel

Santa Monica Mountains

Orange County

Long Beach

Los Angeles

Palos Verdes

Hills

Los Angeles County

Huntington

Beach

EXPLANATION

General head cell

No flow boundary condition

Grid Cell

Pressure

Area

Figure 22. Model grid and boundary conditions for the ground-water simulation model for layer 1, Recent aquifer system (A); layer 2, Lakewood aquifer 

system (B); and layers 3 and 4, Upper San Pedro and Lower San Pedro aquifer systems (C), Los Angeles County, California. 
74 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

0 10 MILES

0 10 KILOMETERS

33°

40'

50'

34°

00'

118° 30' 20' 10' 118° 30'

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Repetto Hills

Elysian

Hills

Merced Hills

San

Valley Gabriel

Santa Monica Mountains

Orange County

Long Beach

Los Angeles

Palos Verdes

Hills

Los Angeles County

Huntington

Beach

EXPLANATION

Puente Hills

Santa Monica

Bay

San Pedro

Bay

Whittier

Narrows

Los Angeles

Narrows

Layer 2

General head cell

No flow boundary condition

Grid Cell

Specified head cell

Model Faults

Puente Hills

Pressure

Area

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 22.—Continued.
Development of a Ground-Water Simulation Model 75

0 10 MILES

0 10 KILOMETERS

33°

40'

50'

34°

00'

118° 30' 20' 10' 118° 00

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Repetto Hills

Elysian

Hills

Merced Hills

Santa Monica Mountains

Orange County

Long Beach

Los Angeles

Palos Verdes

Hills

Los Angeles County

Huntington

Beach

Puente Hills

Santa Monica

Bay

San Pedro

Bay

Whittier

Narrows

Los Angeles

Narrows

Layers 3 and 4

EXPLANATION

Pressure

Area

San

Valley

Gabriel

General head cell

No flow boundary condition

Grid Cell

Specified head cell

Model Faults

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 22.—Continued.
76 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Gabriel

Gabriel

River

San

San

Rio

River

Los

Los

R

River

Angeles

Angeles

Ballona Creek

0 10 MILES

0 10 KILOMETERS

33°

40'

50'

34°

00'

118° 30' 20' 10' 118° 00

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Pressure

Area

Repetto Hills

Elysia

H n ills

Merced Hills

Puente Hills

San

Valley Gabriel

Santa Monica Mountains

Orange County

Los Angeles

Palos Verdes

Hills

Los Angeles County

Dominguez

Hills

EXPLANATION

Santa Monica Bay

San Pedro Bay

Dominguez

Channel

Baldwin

Hills

Beverly

Hills

Inglewood-2 Inglewood-1

Hawthorne-1

Gardena-1

Wilmington-1

Wilmington-2

Willowbrook-1

Los Angeles-1

Huntington

Park-1

Lomita-1 Long

Beach-1

Long Beach-2 Carson-1

South Gate-1

Cerritos-1

Downey-1

La Mirada-1

Lakewood-1

Whittier-1

Rio Hondo-1

Santa Fe

Springs

Pico Rivera-2

Pico Rivera-1

Commerce-1

32A5

31E1

11A2

4C2

22E3

22P4

33L3

33E2

24M3

14J1

6G2

5L1

1A6

35J3

4K1

10G1

26C2

19Q3

19R1

7C1, C2

28H9

32G1 25E1

23B2 21H5

30G1

4K

8L3

14E3

10A1

32C4

36F2

13H3

22L1

9Q1

4K 2N1-4

1F2

21R1

31E3

12K1

20M2

14F2

Unconsolidated deposits

Consolidated rocks

Geology not mapped for

 this study

Los Angeles Basin ground-water simulation boundary

Subbasin boundary within the model

Spreading grounds

USGS multiple-well monitoring site

R15W

R14W

R13W

R12W

R11W

T5S T4S

T3S T2S T1S

Whittier

Narrows

Los Angeles

Narrows

Figure 23. Wells used for water-level calibration and head-dependant boundary conditions for ground-water simulation model, Los Angeles County, 

California.
Development of a Ground-Water Simulation Model 77

All offshore cells in the uppermost layer (either 

layer 1, or layer 2 where layer 1 is not present) are set 

as general-head boundaries to simulate the impact of 

the overlying seawater. At the outermost offshore cells, 

general-head boundaries are specified for all layers. 

For all these offshore general-head boundaries, a 

freshwater-equivalent head based on the bathymetry is 

specified. This equivalent head is a very simplified way 

to account for the impacts of the higher density 

seawater. It is computed as the bathymetric depth 

multiplied by 0.025, the relative density difference 

between seawater and freshwater. The general-headboundary conductance values specified in MODFLOW 

for the outermost offshore cells were 0.006 ft2/s (for 

layer 1 and for layers 2-4 in the Santa Monica Bay) and 

0.003 ft2/s (for layers 2-4 in the San Pedro Bay) 

(fig. 22). Given the average modeled thickness of these 

cells (ranging from 100 to 540 ft), these conductance 

values imply average hydraulic conductivity values at 

these outermost offshore boundaries that range from 

about 0.25 to 2.5 ft/day. General-head-boundary 

conductance values of 0.0001 ft2/s were specified for 

the interior ocean cells in the uppermost active layer. 

Assuming an average vertical distance of about 60 ft 

between these cells and the overlying ocean, these 

conductance values imply average vertical hydraulic 

conductivity values at these interior ocean boundaries 

of about 0.0001 ft/day. The underlying Pico unit (fig. 

3) is considered to be a no-flow boundary. Faults were 

incorporated into the model using the horizontal-flow 

barrier package for MODFLOW (Hsieh and 

Freckleton, 1993).

Model-Layer Elevations

Elevations of the bases of the four aquifer 

systems were determined from the hydrostratigraphy 

analyses described earlier in this report. These 

elevation values were specified in the model (fig. 24) 

and were used to estimate hydraulic conductivity, 

storage coefficient, and vertical conductance; to 

apportion pumpage and injection between model 

layers; and to determine which water-level wells to use 

for each layer in the calibration process. Surfaces of 

model layer elevations were developed by using the 

GIS to interpolate and extrapolate from the elevations 

determined at individual wells. 

Geophysical logs from about 160 wells, 

including 24 USGS monitoring sites, along with about 

90 lithologic logs included in cross sections presented 

by the California Department of Water Resources 

(1961) were used to develop the model layer 

elevations. Depths to the base of the four aquifer 

systems were determined at individual wells. 

Discussion of the criteria used in this analysis is 

included in the earlier section on “Hydrogeologic 

Framework.” In addition to these physical wells, 

21 artificial well locations were used for simple 

extrapolations of the elevation of each layer to the 

edges of the model boundary that were consistent with 

topography and bathymetry. 

To construct a grid to interpolate the surface of 

the base of the four aquifer layers, a separate griding 

program, Surfer 7 (Golden Software, 1999), was used. 

Kriging was chosen as the interpolating algorithm for 

the lower three layers because of the flexibility in 

adjusting the variogram and the fact that kriging allows 

anisotropy, or weighting in divergent directions, in its 

calculations. A summary of the kriging results is in 

Appendix IV. In layer 3 the estimated angle of 

anisotropy was about 180 degrees (north-south); no 

anisotropy was applied in layers 2 or 4. A variogram 

was established for each layer by adjusting the sill, 

correlation length, and nugget effect. Because of its 

limited extent, the Recent aquifer system was 

interpolated using a simple radial basis function. No 

anisotropy was used in the interpolation of the grid.

A grid surface was produced and exported back 

into the GIS, converted into polygon coverages, and 

incorporated into the model input. The top of layers 

2–4 also is the base of the layer above it. Where layer 1 

is not active (fig. 22A), the top of layer 2 is taken to be 

75 ft below land surface. For numerical stability in 

modeling, the base of each model layer was required to 

be a minimum depth below the base of the overlying 

layer (or land surface for layer 1). These minimum 

depths were 100 ft for layer 1, 125 ft for layer 2 and 

75 ft for layers 3 and 4.
78 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

EXPLANATION

Elevation of base of layer – In feet above or below sea level

San Pedro

Bay

Pressure

Area

33°40'

50'

34°

118° 30' 20' 10' 118° 00'

Orange County

Los Angeles

 County

Santa Monica

Bay

Whittier

Narrows

Los Angeles

Narrows

Layer 1

-200 - -100

-100 - 0

0 - 100

100 - 200

200 - 300 -300 - -200

-700 - -600

-600 - -500

-500 - -400

-400 - -300

-800 - -700

-900 - -800

-1,200 - -1,100

-1,100 - -1,000

-1,000 - -900

-1,400 - -1,300

-1,500 - -1,400

-1,600 - -1,500

-1,300 - -1,200

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 24. Elevation of base of layers 1-4 of the ground-water simulation model: Recent aquifer system (A), Lakewood aquifer system (B), Upper San Pedro 

aquifer system (C), and Lower San Pedro aquifer system (D), Los Angeles County, California.
Development of a Ground-Water Simulation Model 79

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

EXPLANATION

Elevation of base of layer – In feet above or below sea level

San Pedro

Bay

Layer 2

33° 40'

34° 00'

50'

118° 30' 20' 10' 118° 00'

Orange County

Los Angeles

 County

Santa Monica

Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

-200 - -100

-100 - 0

0 - 100

100 - 200

200 - 300 -300 - -200

-700 - -600

-600 - -500

-500 - -400

-400 - -300

-800 - -700

-900 - -800

-1,200 - -1,100

-1,100 - -1,000

-1,000 - -900

-1,400 - -1,300

-1,500 - -1,400

-1,600 - -1,500

-1,300 - -1,200

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 24.—Continued.
80 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

-200 - -100

-100 - 0

0 - 100

100 - 200

200 - 300 -300 - -200

-700 - -600

-600 - -500

-500 - -400

-400 - -300

-800 - -700

-900 - -800

-1,200 - -1,100

-1,100 - -1,000

-1,000 - -900

-1,400 - -1,300

-1,500 - -1,400

-1,600 - -1,500

-1,300 - -1,200

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Hollywood

Basin

Whittier

Area

EXPLANATION

Elevation of base of layer – In feet above or below sea level

Orange County

Los Angeles

 County

Santa Monica

Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

Layer 3

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 24.—Continued.
Development of a Ground-Water Simulation Model 81

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast West Coast

Basin

Los Angeles Los Angeles

 County

Pressure

Area

West Coast

Basin

Central

Basin

Hollywood

Basin

Whittier

Area

Orange County

Los Angeles

 County

Santa Monica

Bay

San Pedro Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

D Layer 4

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

-200 - -100

-100 - 0

0 - 100

100 - 200

200 - 300 -300 - -200

-700 - -600

-600 - -500

-500 - -400

-400 - -300

-800 - -700

-900 - -800

-1,200 - -1,100

-1,100 - -1,000

-1,000 - -900

-1,400 - -1,300

-1,500 - -1,400

-1,600 - -1,500

-1,300 - -1,200

Figure 24.—Continued.
82 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Hydraulic Properties

Initial estimates of hydraulic conductivities for 

each layer were calculated by summing the component 

transmissivities presented by the California 

Department of Water Resources (1961) for the relevant 

aquifers in each model layer (fig. 3) and dividing by the 

layer thicknesses. The resulting hydraulic 

conductivities were smoothed by computing the mean 

value within a three-by-three cell neighborhood around 

each cell. These values were modified during 

calibration. The final model-calibrated values used in 

the model are shown in figure 25. Hydraulic 

conductivity values range from 13 to 800 ft/d for 

layer 1, 0.1 to 130 ft/d for layer 2, 0.6 to 140 ft/d for 

layer 3 and 1.0 to 50 ft/d for layer 4. Note, in the model 

calibration, upper bounds of 800, 150, 150, and 50 ft/d 

were fixed for layers 1–4, respectively.

The vertical conductance (Vcont) between the 

aquifers was computed by applying equation 51 of 

McDonald and Harbaugh (1988, p. 5–13). The vertical 

hydraulic conductivity for each model layer was 

computed as a fraction of the horizontal conductivity. 

The applied fractions range from 0.10 in the forebay 

areas to 0.0005 between layers 2 and 3 in the inland 

part of the West Coast Basin. The very small values for 

these ratios reflect the fact that within the thick aquifer 

systems that make up the model layers, the horizontal 

conductance is dominated by the horizontal hydraulic 

conductivity of the continuous coarse-grained deposits, 

and the vertical conductance is dominated by the 

vertical hydraulic conductivity of the fine-grained 

materials. Resulting values for vertical conductance in 

the model are shown in figure 26. Vcont values range 

from 8 x 10-6 to 0.22 /day between layers 1 and 2, 

7 x 10-7 to 7 x 10-2 /day between layers 2 and 3, and 

2 x 10-6 to 4 x 10-2 /day between layers 3 and 4. 

The specific-yield values used for layer 1, which 

are shown in figure 27, were based, in part, on the work 

of the California Division of Water Resources (1934, 

pl. F), which mapped specific yield in the coastal Los 

Angeles area as ranging from 0.15 to 0.23. Specific 

yield values used for layer 1 range from 0.075 to 0.25 

(as shown in figure 27A, specific yield values of .075 

were applied to layer 1 cells outside of the forebay 

areas). For layers 2–4, a specific storage value of 

5.0 x 10-6/ft for layer 2 and 2.0 x 10-6/ft for layers 3–4 

was multiplied by aquifer thickness to obtain the 

confined storage coefficients for each layer. The 

resulting storage coefficient values, shown in 

figure 27B–D range from .0006 to .003 in layer 2, 

.00015 to .0018 in layer 3, and.00015 to.0016 in layer 

4. A constant specific yield of 0.075 was assigned to 

layers 2–4. 

Conductances across the faults were specified in 

the horizontal-flow-barrier package in MODFLOW. 

These conductance values are referred to as hydraulic 

characteristics (Hsieh and Freckleton (1993). Initially, 

hydraulic characteristics for all faults were set at high 

values (1.0 x 10-5/sec) that did not restrict flow. These 

values were modified during model calibration and are 

listed in table 4. Final values applied for hydraulic 

characteristics range from 5.0 x 10-10 to 1.0 x 10-5 /sec.

Areal Recharge

It is assumed that areal recharge occurs in the 

uppermost active model layer. Areal recharge 

represents the combined effects of mountain-front 

recharge on the perimeter of the model domain and 

direct precipitation, return flow from irrigation such as 

lawn watering, and other distributed sources (for 

example, leakage from pipes) within the interior of the 

model domain. Because most parts of the major rivers 

are lined with concrete, river recharge/discharge is not 

simulated in the model. Recharge through the unlined 

channels of the Rio Hondo and San Gabriel River in 

the upper Montebello Forebay (Central Basin) is 

accounted for as part of the artificial spreading 

operations. Note that the potential hydraulic effects of 

the short unlined sections of the San Gabriel and Los 

Angeles Rivers near the San Pedro Bay are not 

simulated in the model. 
Development of a Ground-Water Simulation Model 83

West Coast

Basin

Central

Basin

Santa Monica

Basin

Los Angeles

Forebay Montebello

Forebay

Hollywood

Basin

Whittier

Area

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Orange County

Los Angeles

 County

Whittier

Narrows

Los Angeles

Narrows

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

Layer 1

EXPLANATION

Hydraulic conductivity – In feet per day

1-10

Less than1

11-50

 51-100

101-150

151-200

201-400

400-800

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 25. Hydraulic conductivities for layers 1–4 of the ground-water simulation model: Recent aquifer system (A), Lakewood aquifer system (B), Upper San 

Pedro aquifer system (C), and Lower San Pedro aquifer system (D), Los Angeles County, California.
84 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

0246 8 10 KILOMETERS

0246 8 10 MILES

Pacific

Ocean

B

EXPLANATION

Hydraulic conductivity – In feet per day

1-10

Less than1

11-50

 51-100

101-150

151-200

201-400

400-800

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

Layer 2

West Coast

Basin

Central

Basin

Santa Monica

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Orange County

Los Angeles

 County

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 25.—Continued.
Development of a Ground-Water Simulation Model 85

0246 8 10 KILOMETERS

0246 8 10 MILES

Pacific

Ocean

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

Whittier

Narrows

Los Angeles

Narrows

Layer 3

Pressure

Area

EXPLANATION

Hydraulic conductivity – In feet per day

1-10

Less than1

11-50

 51-100

101-150

151-200

201-400

400-800

Orange County

Los Angeles

 County

West Coast

Basin

Central

Basin

Santa Monica

Basin Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 25.—Continued.
86 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Pacific

Ocean

EXPLANATION

0

0246 8 10 KILOMETERS

246 8 10 MILES

Santa

Monica

Bay

Hydraulic conductivity – In feet per day

1-10

Less than1

11-50

 51-100

101-150

151-200

201-400

400-800

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

Orange County

Los Angeles

 County West Coast

Basin

Central

Basin

Santa Monica

Basin Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Layer 4

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 25.—Continued.
Development of a Ground-Water Simulation Model 87

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Hollywood

Basin

Whittier

Area

Los Angeles

Forebay Montebello

Forebay

Central

Basin

Santa

Monica

Bay

San Pedro

Bay

EXPLANATION

Vertical conductance – (Per day)

Less 10-4

110-4 to 110-3

110-3 to 110-2

110-2 to 110-1

110-1 to 1

1 to 10

A

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33°40'

50'

34°

118°30' 20' 10' 118°

Layer 1

Orange County

Los Angeles

 County

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 26. Vertical conductances for the ground-water simulation model: between layers 1 and 2, Recent and Lakewood aquifer systems (A); between layers 

2 and 3, Lakewood and Upper San Pedro aquifer systems (B); and between layers 3 and 4, Upper San Pedro and Lower San Pedro aquifer systems (C), Los 

Angeles County, California.
88 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Hollywood

Basin

Montebello

Forebay

Central

Basin

0

0246 8 10 KILOMETERS

246 8 10 MILES

EXPLANATION

Vertical conductance – (per day)

Less 10-4

110-4 to 110-3

110-3 to 110-2

110-2 to 1 10-1

110-1 to 1

1 to 10

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

B Layer 2

Orange County

Los Angeles

 County

Whittier

Area

Los Angeles

Forebay

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 26.—Continued.
Development of a Ground-Water Simulation Model 89

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Hollywood

Basin

Whittier

Area

Los Angeles

Forebay

Montebello

Forebay

Central

Basin

0

0246 8 10 KILOMETERS

246 8 10 MILES

Santa

Monica

Bay

San Pedro

Bay

EXPLANATION

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

C Layer 3

Orange County

Los Angeles

 County

Vertical conductance – (per day)

Less 10-4

110-4 to 110-3

110-3 to 110-2

110-2 to 110-1

110-1 to 1

1 to 10

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 26.—Continued.
90 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

EXPLANATION

Specific Yield

0.075

0.1

0.15

0.2

0.25

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

A Layer 1

Orange County

Los Angeles

 County

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los

Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 27. Specific yield for layer 1 and storage coefficients for layers 2–4 of the ground-water simulation model: Recent aquifer system (A), Lakewood aquifer 

system (B), Upper San Pedro aquifer system (C), and Lower San Pedro aquifer system (D), Los Angeles County, California.
Development of a Ground-Water Simulation Model 91

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

EXPLANATION

Storage coefficient

0.0001 - 0.00050

0.00050 - 0.00100

0.00100 - 0.00300

Santa

Monica

Bay

San Pedro

Bay

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

B Layer 2

Orange County

Los Angeles

 County

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 27.—Continued.
92 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean San Pedro

Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

C Layer 3

Orange County

Los Angeles

 County

EXPLANATION

Storage coefficient

0.0001 - 0.00050

0.00050 - 0.00100

0.00100 - 0.00300

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 27.—Continued.
Development of a Ground-Water Simulation Model 93

EXPLANATION

Storage coefficient

0.0001 - 0.00050

0.00050 - 0.00100

0.00100 - 0.00300

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

San Pedro

Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

D Layer 4

Orange County

Los Angeles

 County

Santa Monica

Basin

West Coast

Basin Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 27.—Continued.
94 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Table 4. Hydraulic characteristic values used in the ground-water 

simulation model

Mountain-front recharge is simulated on the 

model perimeter along the foothills bounding the 

model area to the north, northeast, and southwest 

(fig. 28). Estimated values for steady state (1971) 

mountain-front recharge were computed by applying a 

modified version of the Maxey and Eakin (1949) 

method. A description of the approach and steps taken 

to estimate the mountain-front recharge is presented in 

Appendix V. As emphasized in Appendix V, this is a 

very simplified approach with many important 

assumptions. 

For distributed interior recharge in the model for 

the steady state simulation (1971), a value of 1.5 in/yr 

was applied throughout the model domain, except the 

Montebello Forebay where a value of 2 in/yr was 

applied. These very simple estimates of recharge in the 

model interior were based on the measured 

precipitation within the model domain (ranging from 9 

to 16 inches in 1971), along with the likely effects of 

irrigation, pipe leakage, evapotranspiration, and 

amount of impervious area. 

For the transient simulation, the steady-state 

values used in the model for mountain-front recharge 

on the perimeter of the model area and for distributed 

interior recharge were varied annually as a function of 

precipitation. Precipitation station 107D, operated by 

the LACDPW, in Downey was used as an indicator 

station (fig. 1 in Appendix V). Precipitation at station 

107D was normalized by the total precipitation in 

water year 1971 (table 5). For each year of the transient 

simulation, mountain-front and distributed interior 

recharge values were set equal to the steady-state 

values multiplied by the normalized precipitation for 

that year. An upper bound of 1.3 (determined by 

calibration) was placed on the normalized precipitation 

value to reflect the fact that there is a limit to the 

amount of additional precipitation and runoff that will 

replenish the ground-water system. Values used for 

mountain-front recharge and distributed interior 

recharge are summarized in table 5. This recharge is 

incorporated into MODFLOW using the recharge 

package. As is discussed later, there are significant 

limitations in the data and methodology used to 

estimate these recharge values. 

Fault name Model layer(s)

Fault hydraulic 

characteristic

(per second)

Avalon-Compton 2 1 x 10-7

Avalon-Compton 3, 4 1 x 10-9

Baldwin Hills faults 2 1 x 10-9

Baldwin Hills faults 3, 4 5 x 10-10

Cabrillo 2, 3, 4 1 x 10-6

Charnock 2 1 x 10-7

Charnock 3, 4 1 x 10-8

Cherry Hill 2, 3, 4 5 x 10-10

Dominguez anticline 2 1 x 10-7

Dominguez anticline 3, 4 1 x 10-9

Elysian Hills 2, 3, 4 1 x 10-5

Inglewood 2, 3, 4 5 x 10-10

Long Beach 2 1 x 10-8

Long Beach 3, 4 1 x 10-9

Los Alamitos 2 1 x 10-5

Los Alamitos 3, 4 1 x 10-7

Northeast Flank 2, 3, 4 5 x 10-10

Norwalk 2, 3, 4 1 x 10-8

Offshore faults 2, 3, 4 1 x 10-5

Overland 2, 3, 4 1 x 10-8

Palos Verdes 2, 3, 4 1 x 10-5

Pico 2, 3, 4 1 x 10-5

Poretero Canyon 2, 3, 4 5 x 10-10

Portero 2, 3, 4 5 x 10-10

Railroad Grade 2, 3, 4 5 x 10-10

Reservoir Hill 2, 3, 4 5 x 10-10

Rio Hondo 2, 3, 4 1 x 10-5

Roscrans anticline 

and faults

2 1 x 10-7

Roscrans anticline 

and faults

3, 4 1 x 10-8

Santa Monica 2, 3, 4 1 x 10-7

Santa Monica, 

unnamed

2, 3, 4 1 x 10-5

Seal Beach 2, 3, 4 5 x 10-10
Development of a Ground-Water Simulation Model 95

Pacific

Ocean

Santa

 Monica

 Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Repetto Hills

Elysi

H

an

ills

Merced Hills

33°

40'

50'

34°

00'

118° 30' 20' 10' 118° 00'

San Gabriel Valley

Santa Monica Mountains

Orange County

Long

Beach

Los

Angeles

Palos Verdes

Hills

Los Angeles County

Signal

Hill

Dominguez

Hills

Seal Beach

Huntington

Beach

0 10 MILES

0 10 KILOMETERS

EXPLANATION

Santa

Monica

Bay

San

Pedro

Bay

Rio Hondo spreading cell

San Gabriel spreading cell

Mountain front recharge cell

Injection cells

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

Puente Hills

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 28. Injection, spreading, and mountain-front recharge cells for the ground-water simulation model, Los Angeles County, California.
96 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Table 5. Annual precipitation at LACDPW Downey Station 107D and recharge and pumpage used in ground-water simulation model

[Acre-ft/yr, acre-feet per year]

Water 

year

Precipitation

(inches)

Normalized 

precipation

Mountain front

and interior

 recharge

 (acre-ft/yr)

Spreading

(acre-ft/yr) 

Injection

(acre-ft/yr) 

Pumpage

(acre-ft/yr) 

1971 11.46 1 64,400 121,700 36,200 278,300

1972 6.4 .56 36,100 62,900 41,000 289,300

1973 18.63 1.63 83,700 147,100 41,800 272,300

1974 14.55 1.27 81,800 123,900 42,700 274,000

1975 15.01 1.31 83,700 105,700 36,900 278,500

1976 9.58 .84 54,100 81,900 44,800 283,200

1977 11.24 .98 63,100 69,900 49,300 279,000

1978 33.86 2.95 83,700 170,700 40,200 259,600

1979 18.69 1.63 83,700 151,800 34,500 270,700

1980 28.29 2.47 83,700 137,100 37,200 272,300

1981 8.74 .76 48,900 128,400 34,400 275,800

1982 13.41 1.17 75,300 110,100 34,300 276,500

1983 30.32 2.65 83,700 165,200 45,200 261,400

1984 11.99 1.05 67,600 114,500 39,500 258,300

1985 12.45 1.09 70,200 110,200 37,500 256,900

1986 19.47 1.7 83,700 117,400 31,700 264,600

1987 6.49 .57 36,700 101,000 39,400 254,000

1988 11.47 1 64,400 100,300 37,500 254,300

1989 7.82 .68 43,800 123,900 33,500 252,100

1990 7.87 .69 44,400 132,700 32,100 245,200

1991 12.22 1.07 68,900 138,700 29,700 247,900

1992 16.07 1.4 83,700 152,800 34,800 260,500

1993 26.56 2.23 83,700 174,500 31,300 226,800

1994 9.26 .81 52,200 113,600 25,100 181,100

1995 26.17 2.28 83,700 151,700 23,200 235,300

1996 10.68 .93 59,900 130,500 23,300 238,800

1997 13.95 1.22 78,600 128,300 29,300 243,800

1998 32.45 2.83 83,700 133,200 25,400 244,500

1999 7.29 .64 41,200 80,400 27,300 259,700

2000 9.21 .8 51,500 108,900 30,400 254,200

Mean 15.39 1.34 67,500 123,000 35,000 258,300
Development of a Ground-Water Simulation Model 97

Pumpage, Spreading, and Injection

The model incorporates data on pumpage, 

spreading, and injection provided by the WRDSC, Los 

Angeles County Department of Public Works 

(LACDPW), the city of Santa Monica, and the 

California Department of Water Resources. Pumpage 

records for the West Coast and Central Basins have 

been maintained since the early 1960s by the California 

Department of Water Resources, which has served as 

water master. These pumpage data, along with data 

from the Santa Monica Basin (provided by the city of 

Santa Monica), were used in the model. Pumpage for 

wells perforated in more than one layer was divided 

between layers on the basis of perforation information 

and hydraulic conductivities and elevations of each 

model layer. Where perforation data were not available 

for a given well, water in that well was distributed 

between model layers on the basis of the average 

distribution for other wells in that area in that year. 

This dividing of pumpage between layers was done 

iteratively during calibration as hydraulic-conductivity 

values were adjusted. Model cells with pumpage in at 

least one stress period are shown in figure 29. Pumpage 

was incorporated into MODFLOW using the well 

package. Note that the well package does not have the 

capability of reapportioning pumpage between layers 

when a cell in a layer becomes dry during the 

simulation. Annual values input for pumpage are given 

in table 5. 

Artificial recharge in the model includes 

spreading in the Montebello Forebay and direct 

injection at the three barrier projects: the West Basin 

Barrier and the Dominguez Gap Barrier in the West 

Coast Basin and the Alamitos Barrier in the Central 

Basin (fig. 28). Annual values for spreading and 

injection are given in table 5. Reported total annual 

spreading rates for the Rio Hondo and San Gabriel 

spreading facilities are incorporated into the model as 

recharge to layer 1 in the cells shown in figure 28 using 

the recharge package in MODFLOW. Total amounts of 

injection are reported for each of the three barrier 

projects. These injection totals are prorated among 

individual wells based on periodic well measurements. 

As was done with pumpage, injected water was 

distributed between model layers on the basis of the 

perforations of the injection well and the aquifer 

conductivities and elevations. Injection was 

incorporated into MODFLOW using the well package. 

Model Calibration

The steady-state and transient calibrations were 

done in a coupled, iterative manner. Water year 1971 

(October, 1970 to September, 1971) was chosen as an 

approximate representation of steady-state conditions. 

The goal was to identify an interval during the modern 

period (after the basins were adjudicated) when 

accurate pumpage data were available and groundwater levels were relatively constant. Analysis of longterm hydrographs indicated that water year 1971 was 

the most appropriate choice. It was the earliest year 

after the dramatic water-level recovery resulting from 

adjudication in which water levels had somewhat 

stabilized at many wells. However, it is certain that 

ground-water conditions were not at a true equilibrium 

in 1971 (fig. 7), nor at any other time after the initiation 

of ground-water development in the area. The 30-year 

transient simulation period was considered adequate to 

minimize most residual effects of the initial conditions. 

Water-level data for calibrating the model were 

compiled from LACDPW, the WRDSC, and the city of 

Santa Monica, and from USGS monitoring wells. The 

locations of the wells used for model calibration are 

shown in figure 23.

Shown in figure 30 are simulated steady-state 

ground-water levels for water year 1971, along with 

average measured water levels for the water year in the 

four model layers representing the four aquifer 

systems. Note that most measured water-level data for 

1971 is for layer 3. The transient calibration used the 

simulated 1971 water levels as initial conditions. 

Transient hydrographs for the 1971–2000 

transient simulation are shown in Appendix VI. 

Contours of simulated and average measured water 

levels for water year 2000 are shown in figure 31.
98 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Whittier

Area

Hollywood

Basin

Pressure Area

EXPLANATION

Pumping cells

San

Pedro

Bay

Santa

Monica

Bay

Whittier

Narrows

Los Angeles

Narrows

 40'

50'

° 00'

118° 00' 20' 10' 118° 00'

Orange County

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 29. Pumping cells for years 1971–2000 in ground-water simulation model, Los Angeles County, California.
Development of a Ground-Water Simulation Model 99

80

300

40

-40

-20

-25

0

0

0

120

140

160

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

50

81

193

326

EXPLANATION

Dry cells

50

Simulated water-level contour - Shows water level 

in feet above sea level. Contour interval 20 feet

Water-level measurement - In feet above sea level

130

Dry cells

Grid cell

Model Boundary

Santa

Monica

Bay

San Pedro Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

A Layer 1

Orange County

Los Angeles

 County

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 30. Model-simulated and average measured water levels, 1971, for layers 1–4 of the ground-water simulation model: Layer 1, Recent aquifer system 

(A); Layer 2, Lakewood aquifer system (B); Layer 3, Upper San Pedro aquifer system (C); and Layer 4, Lower San Pedro aquifer system (D), Los Angeles County, 

California.
100 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

0

0246 8 10 KILOMETERS

246 8 10 MILES

Santa

M ionca M i

B y

S Pd B an Ped o Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

B Layer 2

Orange County

Los Angeles

 County

EXPLANATION

Dry cells

50

Simulated water-level contour - Shows water level 

in feet above sea level. Contour interval 20 feet

Water-level measurement - In feet above sea level

130

Dry cells

Grid cell

Model Boundary

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

80

40

40

40

40

-40

-40

-80

0

0

0

0 0

0

0

0

-40

-40

-40

-40

-40

-40

-40 -40

27 8

-6

2

118

109

120

340

300

300

360

120

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 30.—Continued.
Development of a Ground-Water Simulation Model 101

-28

-97

-47

-54

-45

-35

-2

-7

-69

-64

-17

-39

-44

-74

-63

-68

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

0

0246 8 10 KILOMETERS

246 8 10 MILES

S t n

Monica

Bay

San Pedro Bay an Pedr Ba

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

C Layer 3

Orange County

Los Angeles

 County

EXPLANATION

Dry cells

50

Simulated water-level contour - Shows water level 

in feet above sea level. Contour interval 20 feet

Water-level measurement - In feet above sea level

130

Dry cells

Grid cell

Model Boundary

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

80

80

80

-80

-80

-80 -80

-40

40

40

-60

40

-40

-40

-40

-40

0

0

80

80

-40

0

0

0

0

0

0

-40

40

40

-40

-40

-40

-40

-40

120

120

160

120

160

300

-80

-80

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 30.—Continued.
102 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Santa

Monica

Bay

San Pedro Bay San Ped o Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

D Layer 4

Orange County

Los Angeles

 County

EXPLANATION

Dry cells

50

Simulated water-level contour - Shows water level 

in feet above sea level. Contour interval 20 feet

Water-level measurement - In feet above sea level

130

Dry cells

Grid cell

Model Boundary

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

-68

-19

80

80

-80

40

40

40

40

80

80

-40

-40

-40

0

0

0

0

0

0

0

0

-60

-80

160

300

-100

-40

-40

-40

-40

-40

-40

-40

120

160

120

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 30.—Continued.
Development of a Ground-Water Simulation Model 103

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay Montebello

Forebay

Hollywood

Basin

Whittier

Area

0

0246 8 10 KILOMETERS

246 8 10 MILES

Santa

Monica

Bay

San Pedro Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

A Layer 1

Orange County

Los Angeles

 County

EXPLANATION

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

Dry cells

50

Simulated water-level contour - Shows water level 

in feet above sea level. Contour interval 20 feet

Water-level measurement - In feet above sea level

130

Dry cells

Grid cell

Model Boundary

12

50

79

63

110 84 100

300

180

60

60

20

0

20

-20 -20

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 31. Model-simulated and average measured water levels, 2000, for layers 1–4 of the ground-water simulation model: Layer 1, Recent aquifer system 

(A); Layer 2, Lakewood aquifer system (B); Layer 3, Upper San Pedro aquifer system (C); and Layer 4, Lower San Pedro aquifer system (D), Los Angeles County, 

California.
104 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

0

0246 8 10 KILOMETERS

246 8 10 MILES

Santa

M i n a

B y

San Pedro Bay an Pedr Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

B Layer 2

Orange County

Los Angeles

 County

EXPLANATION

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

Dry cells

50

Simulated water-level contour - Shows water level 

in feet above sea level. Contour interval 20 feet

Water-level measurement - In feet above sea level

130

Dry cells

Grid cell

98 81

117

62

106

-26

191

17

-17

0

-3 -27

-24

-27

-12

-22

39

16

-15

-15 -17

0

216

-28

-5

45

80

80

80

80

120 300

300

340

340

40

40

40

40

40 200

200

40

80

-40

-40

0

0

0

0

0

0

0

120

120

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 31.—Continued.
Development of a Ground-Water Simulation Model 105

73

1

39

92

136

37

135 -43

-47

-8

61

-34

-35

-56

0

-72 -65

-72

-25 -6

-60

-72

-86 -98

-43

-40

-28

-21

-22

-26

33

-18

-21

-40

7

-80

132

-31 -43

-6

-4

-98

14

80

80

120

80 80

120

120

40

40

40

40

-40

-40

-80

-80

-80

-40

300

180

0

-40

-40

-20

-20

40

40

80

-40

-40

0

0

0

0

0 0

-40

0

0

120

0

0246 8 10 KILOMETERS

246 8 10 MILES

-58

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay Whittier

Area

Hollywood

Basin

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

C Layer 3

Orange County

Los Angeles

 County

Santa

Monica

Bay

San Pedro Bay

EXPLANATION

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

Dry cells

50

Simulated water-level contour - Shows water level 

in feet above sea level. Contour interval 20 feet

Water-level measurement - In feet above sea level

130

Dry cells

Grid cell

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 31.—Continued.
106 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

EXPLANATION

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

Dry cells

50

Simulated water-level contour - Shows water level 

in feet above sea level. Contour interval 20 feet

Water-level measurement - In feet above sea level

130

Dry cells

Grid cell

77

137

65

81

-23

-23

-41

-24-25

0

-44 -86

-72

-52

-32

-51

0

-9

-22

-51

-42

84

80

80

80

300

40

40

40

40

40

40

80

120

160

40

80

-40

-80

-40

-40

-40

0

0

0

0

0

0

-40

-40

-40

-40

-40

-20

-40

-40

-40

0

120

120

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

0

0246 8 10 KILOMETERS

246 8 10 MILES

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

D Layer 4

Orange County

Los Angeles

 County

Santa

Monica

Bay

San Pedro Bay

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Figure 31.—Continued.
Development of a Ground-Water Simulation Model 107

The strategy for calibration was to achieve the 

best possible match to measured water levels at the 

USGS multiple-well monitoring sites drilled for this 

study and at selected long-term monitoring wells used 

by local agencies. Parameters varied as part of the 

calibration included hydraulic conductivity, vertical-tohorizontal hydraulic-conductivity ratios, specific yield, 

and selected hydraulic characteristics. 

Hydraulic conductivities in the Montebello 

Forebay were increased from their initial values (by 

factors of 2.5 and 1.5 for layers 1–3 and 4, 

respectively) in order to match measured water levels, 

given the large quantities of artificially recharged water 

moving out through that area. Initial values of 

hydraulic conductivity in layers 1 and 2 in the Los 

Angeles Forebay also were increased by a factor of 2.0 

near the Los Angeles Narrows and 1.5 elsewhere. 

Initial values of hydraulic conductivity in layers 3 and 

4 in the Los Angeles Forebay were decreased to 0.15 

times their initial values in order to simulate the 

depressed water levels in the lower aquifers in that 

area. In the Central Basin Pressure Area downgradient 

from the forebays, hydraulic conductivities in layers 1 

and 3 were increased from their initial values by factors 

of 1.5 and 2.0, respectively. As in the Montebello 

Forebay, this increase was necessary to match water 

levels given the large flows of water flowing into the 

Central Basin Pressure Area from the Montebello 

Forebay. Hydraulic conductivities in the southwestern 

part of the Central Basin Pressure Area adjacent to the 

NIU were reduced to about 0.20 times their initial 

values in layers 3 and 4. This was required to simulate 

the depressed water levels in this region. Hydraulic 

conductivities also were reduced from their initial 

values in all active layers of the Whittier area (0.5 and 

0.05 times initial values in layers 1 and 2-4, 

respectively), Hollywood subbasin (0.50 times initial 

values), Santa Monica Basin (0.25 times initial values), 

and West Coast Basin (0.30 times initial values in the 

area between the Charnock Fault and the NIU and 0.65 

times initial values elsewhere).

Modification of hydraulic characteristics in the 

MODFLOW horizontal-flow-barrier package focused 

on a small subset of the faults included in the model. 

The initial hydraulic characteristics of the faults and 

folds making up the NIU were reduced to match the 

overall regional gradient across the NIU between the 

Central and West Coast Basins (fig. 2A, table 4). The 

hydraulic characteristics of the Santa Monica and 

Portrero Canyon Faults (fig. 2A, table 4) were reduced 

to improve the simulation of water-level gradients 

across the Santa Monica Basin. The hydraulic 

characteristics of the Norwalk Fault were reduced to 

improve the simulation of water levels in and 

downgradient from the Whittier area. The hydraulic 

characteristics of the Charnock and Overland Faults 

also were reduced to provide better simulation of water 

levels in the area between these faults and the NIU. 

Vertical-conductance values were modified (by 

modifying the vertical-to-horizontal hydraulic 

conductivity ratios) to match the vertical differences in 

water levels measured at the USGS monitoring sites. 

High vertical-conductance values were required in the 

upgradient part of the Montebello Forebay area; these 

values are consistent with the lack of confining layers 

between the aquifers in that area. The greatest 

reduction in vertical- conductance values was required 

between layer 2 (the Lakewood aquifer system) and 

layer 3 (the Upper San Pedro aquifer system) in the 

eastern (inland) part of the West Coast Basin to better 

simulate the vertical discontinuity in water levels 

observed at USGS monitoring sites at Inglewood-1 

(2S/14W-28M5–7), Carson-1(4S/13W-9H9–12), and 

Gardena-1(3S/14W-13J6–8) (fig. 23)(note that the 

model still underestimates the vertical gradients 

between layers 2 and 3 at these sites). 

Specific yield in layer 1 was varied by zones 

(4 zones for the Montebello Forebay, 2 zones for the 

Los Angeles Forebay, and 1 zone for all non-forebay 

areas). As stated earlier, a single value of specific yield 

was applied to layers 2–4 for the entire model area. The 

model was somewhat sensitive to values of specific 

yield in the Montebello Forebay area. The maximum 

specific-yield value in the Montebello Forebay was set 

at 0.25. When this value was lowered, the model 

overestimated transient water level responses to annual 

changes in spreading quantities. The amplitude of 

annual water-level fluctuations also was sensitive to 

the non-forebay specific yield in layer 1 and to the 

specific yield specified for layers 2-4. Values for 

specific storage were modified little during the 

calibration. 
108 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

In general, results shown in figures 30, 31, and 

Appendix VI indicate that the simulation model 

provides a reasonable representation of the regional 

ground-water system. Vertical differences between 

water levels in the four aquifer systems are generally 

simulated well (see the USGS multiple-well 

monitoring sites in Appendix VI). The model also 

matches the historical transient changes in water levels 

over the 30-year simulation period well. There 

undoubtedly are local features that are not captured by 

the model. The sum-of-squared errors (SS) was 

computed by 

(1)

where

Root-mean-square error is related to the sumof-squared error by 

 (2)

The average error (AE) is: 

 (3)

A total of 942 measurements of water levels in 

the Central and West Coast Basins were used (fig. 23) 

(the six wells in the Hollywood and Santa Monica 

Basins were excluded). These are average annual water 

levels that range from 109 ft below mean sea level to 

158 above mean sea level, a range of 267 ft. The 

RMSE for the model is 16.4 ft. The average error is 1.2 

ft. A plot of simulated and measured water levels for 

the calibration wells is shown in figure 32.

When interpreting the model results, applying 

the model, and considering future modifications of the 

model, it is important to keep in mind several features 

that are less accurately simulated by the model. These 

features are summarized below and can be seen from 

examining Appendix VI and figures 30–31. See 

figure 23 for well locations. 

Water levels are overestimated in parts of 

Montebello Forebay. (for example, USGS monitoring 

sites Rio Hondo-1 (layers 2–4, wells 

2S/12W-26D9–13) and Pico Rivera-2 (layer 4, well 

2S/12W-25G3) and the Los Angeles Forebay (layer 3, 

well 2S/13W-10A1). On the boundary of the Whittier 

area, the model underestimates water levels in layer 4 

at the USGS Santa Fe Springs-1 monitoring site 

(3S/11W-9D2). Note that at this site, measured water 

levels in layer 4 are significantly above those in layer 3 

(3S/11W-9D3–4) and are similar to those measured in 

the deepest piezometer at this site (which is considered 

to be in the Pico unit). Pressurized gas was encountered 

in this deepest piezometer. 

In the northwest part of the Central Basin 

Pressure Area the model overestimates water levels in 

layer 4 in well 2S/14W-14F2. This well is included as a 

calibration well because it has been used as a long-term 

monitoring well. There is no perforation information 

for the well, but based on its depth (954 ft) it is 

assumed to represent layer 4. At the USGS 

Inglewood-2 monitoring site (2S/14W-26N5–6), also 

located in the northwest part of the Central Basin 

Pressure Area, the model underestimates water levels 

in layer 3. This monitoring site is located very close to 

the NIU. 

In the southern part of the Central Basin Pressure 

Area, the model underestimates water levels in layer 4 

at 4S/12W-25E1. At the USGS Lakewood-1 

monitoring site, the model does not match the extreme 

decline in water levels in layers 3 and 4 at the very end 

of the simulation period (4S/12W-5H5–7). This 

drawdown is the result of a new production well, 

located within 100 ft of the monitoring wells, going 

online in water year 1998. Such pumping well effects 

cannot be simulated in a regional model such as this. 

nwl = the total number of water-level 

comparisons

= the kth simulated water level, in feet, and 

hk = the kth measured water level, in feet

SS hˆ

k hk ( ) – 2

k = 1

nwl

= ∑

h

ˆ

k

RMSE SS

nwl = --------

AE ( ) 1 ⁄ nwl hk

ˆ hk ( ) –

k = 1

nwl

= ∑
Development of a Ground-Water Simulation Model 109

-200

-100

100

200

SIMULATED WATER LEVEL, IN FEET

Layer 1 Layer 3

Layer 2 Layer 4

-200

-100

100

200

-200 -100 Sea Level

Sea

Level

Sea

Level

100 200 Sea Level

SIMULATED WATER LEVEL, IN FEET

-200 -100 100 200

MEASURED WATER LEVEL, IN FEET MEASURED WATER LEVEL, IN FEET

Figure 32. Simulated water levels as a function of measured water levels at calibration wells, model layers 1–4, Los Angeles County, California.
110 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

In the inland part of the West Coast Basin, 

adjacent to the NIU, water levels are slightly 

underestimated in layer 2 [for example, USGS 

monitoring sites at Inglewood-1 (2S/14W-28M7), 

Carson-1(4S/13W-9H12), and Gardena-1 

(3S/14W-13J8)]. In the southern part of the West Coast 

Basin, near the Dominguez Gap Barrier project, water 

levels are slightly underestimated in layer 2 at USGS 

monitoring site at Wilmington-2 (4S/13W-32F5) and 

overestimated in layer 4 at USGS monitoring site 

Wilmington-1 (4S/13W-28A3–4). In the middle of the 

West Coast Basin, the model slightly underestimates 

water levels in layer 3 at monitoring wells PM-3 

Madrid and PM-4 Mariner.

Although the primary goal of the model is to 

simulate water levels in the Central and West Coast 

Basins, water levels in the Santa Monica Basin also 

were compared. In the Santa Monica Basin, comparing 

simulated and measured water levels is complicated by 

the fact that most of the reported water levels were 

measured under pumped conditions. Pumping ceased 

in the Charnock well field in 1996. Post-1996 modelsimulated water levels are slightly higher than the 

measured water levels for recent years in well 

2S/15W-11A1 (Charnock -18). There has been very 

little pumpage from the ARC well field in recent years. 

The model appears to underestimate recent water levels 

at 1S/15W-32A5 (ARC-4). Active pumping continues 

at wells 2S/15W-4C2 (SM3) and 1S/15W-31E1 (SM1).

In addition to identifying areas where there are 

differences between simulated and measured water 

levels in particular model layers, it is also important to 

identify areas where there are differences between 

different measured water levels within the same model 

layer. Most of the USGS monitoring sites have 

multiple wells within layer 3—the Upper San Pedro 

aquifer system. In several of these—Carson-1

(4S/13W-9H9–11), Wilmington-1 (4S/13W-28A5–6), 

Inglewood-1(2S/14W-28M5–6), and LongBeach-2(4S/13W-1N5–6)—there is a noticeable 

difference in measured water levels in layer 3 wells 

(Appendix VI). This indicates that in these parts of the 

study area, the shallower part of the upper San Pedro 

aquifer system (the Lynwood aquifer) has a hydraulic 

response that is different from that of the deeper part of 

the Upper San Pedro aquifer system (the Silverado 

aquifer) (fig. 3). At two monitoring sites, Downey-1 

(3S/12W-9J4–5) and Hawthorne-1 (3S/14W-17G7–8), 

there are differences between measured water levels in 

layer 2 wells. 

Model-Parameter Sensitivity

A sensitivity analysis was done by independently 

varying 74 parameters to determine how parameter 

estimates affected simulation results. Model sensitivity 

was described in terms of RMSE. Parameter values 

were multiplied by 0.2 to 5 times the calibrated 

estimates. Changes in RMSE for all 74 parameters at 

0.2 and 5 times the calibrated estimate are summarized 

in table 6. Although 74 parameters are presented in this 

sensitivity analysis, a much more limited number of 

parameters were systematically varied as part of the 

model calibration (see previous discussion). Variations 

in computed RMSE for a range of factors for selected 

model parameters are shown in figure 33.

Hydraulic conductivities of layer 3 in the West 

Coast Basin, layers 1 and 3 in the Montebello Forebay, 

and layer 3 of the Central Basin Pressure Area were 

among the most sensitive parameters (table 6). The 

model was sensitive to hydraulic conductivity of 

layer 3 in the West Coast Basin and Central Basin 

Pressure Area because most pumpage is drawn from 

layer 3 (Upper San Pedro Aquifer system) in these two 

areally extensive zones that include many of the 

available observations. The model was sensitive to 

hydraulic conductivities in the Montebello forebay 

because these parameters controlled the availability of 

water to all downgradient areas. 

The model was fairly sensitive to changes in all 

of the recharge parameters (table 6). Other than 

adjusting the bound set on maximum rates, recharge 

was not treated as a model calibration parameter. 

Model sensitivity to individual parameter changes was 

asymmetric about the calibrated value for almost all the 

parameters that were evaluated (fig. 33, table 6). For 

example, increases in recharge affected RMSE much 

more than decreases in recharge. As shown in table 6, 

the RMSE is relatively insensitive to the hydraulic 

characteristics of faults over the range of values tested. 

Among the four fault sets tested, the model is most 

sensitive to large reductions in the hydraulic 

characteristic of the Charnock and Overland Faults 
Development of a Ground-Water Simulation Model 111

(note that figure 33 shows variations in computed RMSE for these faults over a wider range—from 0.01 to 100 

times calibrated value—than other parameters). 

Table 6. Sensitivity of model parameters—Continued

Parameter name

Change in RMSE from calibrated estimate Maximum 

absolute 

change 0.2 X 5 X

Hydraulic conductivity of layer 3 in the West Coast Basin 20.22 4.49 20.22

Hydraulic conductivity of layer 1 in the Montebello Forebay 5.34 18.15 18.15

Hydraulic conductivity of layer 3 in the Montebello Forebay 6.83 17.32 17.32

Recharge of layer 2 in the Los Angeles Forebay 1.53 13.66 13.66

Recharge of layer 2 in the Central Basin Pressure area 1.10 13.22 13.22

Hydraulic conductivity of layer 3 in the Central Basin Pressure area 12.61 7.60 12.61

Recharge of layer 2 in the Hollywood Basin 1.02 11.41 11.41

Recharge of layer 2 in the West Coast Basin 1.91 11.17 11.17

Recharge of layer 2 in the Santa Monica Basin .90 10.15 10.15

Specific Yield 4.90 1.07 4.90

Hydraulic conductivity of layer 3 in the Los Angeles Forebay 4.64 .07 4.64

Hydraulic conductivity of layer 2 in the Los Angeles Forebay 1.48 4.52 4.52

Hydraulic conductivity of layer 4 in the Montebello Forebay .70 3.76 3.76

Vertical leakance (Vcont) of layer 2 in the Whittier area 3.09 −.29 3.09

Hydraulic conductivity of layer 2 in the Montebello Forebay .68 2.92 2.92

Recharge of layer 2 in the Montebello Forebay .15 2.26 2.26

Hydraulic conductivity of layer 4 in the Central Basin Pressure area 1.98 1.41 1.98

Hydraulic conductivity of layer 2 in the Whittier area 1.53 −.31 1.53

Vertical leakance (Vcont) of layer 2 in the Central Basin Pressure area 1.32 .67 1.32

Recharge of layer 2 in the Whittier area .13 1.16 1.16

Hydraulic conductivity of layer 1 in the Central Basin Pressure area .81 1.07 1.07

Hydraulic conductivity of layer 3 in the Whittier area .92 −.19 .92

Hydraulic conductivity of layer 2 in the Central Basin Pressure area .29 .84 .84

Vertical leakance (Vcont) of layer 2 in the West Coast Basin .75 .62 .75

Hydraulic conductivity of layer 4 in the West Coast Basin .05 .44 .44

Hydraulic conductivity of layer 4 in the Los Angeles Forebay .32 .10 .32

Vertical leakance (Vcont) of layer 2 in the Montebello Forebay −.28 .15 .28

Vertical leakance (Vcont) of layer 3 in the Central Basin Pressure area .25 −.17 .25

Vertical leakance (Vcont) of layer 3 in the Los Angeles Forebay .25 .00 .25

Hydraulic conductivity of layer 3 in the Santa Monica Basin −.25 −.10 .25

Vertical leakance (Vcont) of layer 1 in the West Coast Basin .24 −.04 .24

Hydraulic conductivity of layer 3 in the offshore-San Pedro Bay .20 −.03 .20

Vertical leakance (Vcont) of layer 2 in the Los Angeles Forebay .20 −.07 .20

Hydraulic conductivity of layer 4 in the Whittier area .17 −.13 .17

Hydraulic conductivity of layer 2 in the West Coast Basin .12 .17 .17

Vertical leakance (Vcont) of layer 1 in the Montebello Forebay −.13 .03 .13

Vertical leakance (Vcont) of layer 3 in the Whittier area .11 .00 .11

Table 6. Sensitivity of model parameters

[RMSE, root mean squared error, in feet] 
112 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Hydraulic conductivity of layer 1 in the West Coast Basin −.01 −.10 .10

Vertical leakance (Vcont) of layer 1 in the Central Basin Pressure area .07 −.02 .07

Storage coefficient in Layer 3 .03 −.06 .06

Hydraulic conductivity of layer 4 in the Santa Monica Basin .06 −.06 .06

Vertical leakance (Vcont) of layer 3 in the West Coast Basin .06 .01 .06

Hydraulic characteristic of Charnock and Overland Faults −.05 .06 .06

Vertical leakance (Vcont) of layer 1 in the Los Angeles Forebay −.05 −.01 .05

Hydraulic characteristic of faults along Newport-Inglewood uplift 0.03 −0.05 0.05

Storage coefficient in Layer 2 .01 −.05 .05

Hydraulic conductivity of layer 2 in the Hollywood Basin −.04 .04 .04

Hydraulic conductivity of layer 4 in the offshore-San Pedro Bay .04 −.03 .04

Hydraulic conductivity of layer 3 in the Hollywood Basin −.03 .04 .04

Hydraulic conductivity of layer 4 in the offshore-North Santa Monica Bay .04 −.01 .04

Hydraulic characteristic of Norwalk fault .03 .03 .03

Hydraulic conductivity of layer 2 in the Santa Monica Basin −.01 −.03 .03

Vertical leakance (Vcont) of layer 3 in the Montebello Forebay −.03 .01 .03

Storage coefficient in Layer 4 .01 −.03 .03

Conductance of South Monica and Portero Canyon Faults −.03 −.02 .03

Vertical leakance (Vcont) of layer 2 in the Hollywood Basin .03 −.01 .03

Hydraulic conductivity of layer 4 in the Hollywood Basin −.01 .03 .03

Hydraulic conductivity of layer 2 in the offshore-San Pedro Bay .01 −.03 .03

Vertical leakance (Vcont) of layer 2 in the Santa Monica Basin .022 .011 .022

Vertical leakance (Vcont) of layer 2 in the offshore-San Pedro Bay .020 .002 .020

Hydraulic conductivity of layer 3 in the offshore-North Santa Monica Bay .018 −.014 .018

Vertical leakance (Vcont) of layer 1 in the offshore-San Pedro Bay .018 .000 .018

Hydraulic conductivity of layer 3 in the offshore-South Santa Monica Bay .006 −.015 .015

Vertical leakance (Vcont) of layer 3 in the Santa Monica Basin −.010 .011 .011

Hydraulic conductivity of layer 4 in the offshore-South Santa Monica Bay .010 −.004 .010

Vertical leakance (Vcont) of layer 2 in the offshore-North Santa Monica Bay −.009 −.003 .009

Hydraulic conductivity of layer 2 in the offshore-South Santa Monica Bay .001 −.007 .007

Vertical leakance (Vcont) of layer 3 in the offshore-South Santa Monica Bay .006 .000 .006

Vertical leakance (Vcont) of layer 2 in the offshore-South Santa Monica Bay .001 −.005 .005

Vertical leakance (Vcont) of layer 3 in the offshore-San Pedro Bay −.004 .002 .004

Vertical leakance (Vcont) of layer 1 in the Whittier area .003 .003 .003

Hydraulic conductivity of layer 2 in the offshore-North Santa Monica Bay .002 −.003 .003

Vertical leakance (Vcont) of layer 3 in the offshore-North Santa Monica Bay .000 −.002 .002

Vertical leakance (Vcont) of layer 3 in the Hollywood Basin −.001 −.001 .001

Table 6. Sensitivity of model parameters—Continued

Parameter name

Change in RMSE from calibrated estimate Maximum 

absolute 

0.2 X 5 X change
Development of a Ground-Water Simulation Model 113

Charnock and Overland

Fault conductance

15

20

25

30

35

40

0.01 0.1 1 10 100

15

20

25

30

35

40

20

25

30

35

40

20

25

30

35

40

0.1 1 10 0.1 1 10

15

15

PARAMETER MULTIPLIER

Hydraulic conductivity of layer 1

 in the Montebello Forebay

Hydraulic conductivity of layer 3

in the Central Basin Pressure Area

Hydraulic conductivity of

 layer 3 in the 

 West Coast Basin

Hydraulic conductivity of layer 2

 in the Los Angeles Forebay

Hydraulic conductivity of layer 2

in the Whittier Area

Hydraulic conductivity of layer 2

in the Montebello Forebay

Hydraulic conductivity of layer 3 

in the Los Angeles Forebay

Hydraulic conductivity of layer 3 

in the Santa Monica Basin

Hydraulic conductivity of layer 4

in the Central Basin Pressure Area

Hydraulic conductivity of layer 4

in the Montebello Forebay

15

20

25

30

35

40

15

20

25

30

35

40

20

25

30

35

40

20

25

30

35

40

20

25

30

35

40

0.1 1 10

15

15 15

15

20

25

30

35

40

20

25

30

35

40

ROOT MEAN SQUARE ERROR, IN FEET

Figure 33. Sensitivity graphs for selected model parameters. 
114 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Vertical Leakance (Vcont) of

layer 2 in the Whittier Area

Vertical Leakance (Vcont) of layer 2 

in the Central Basin Pressure Area 

Vertical Leakance (Vcont) of

layer 2 in the West Coast Basin

Storage Coefficient in Layer 2

Storage Coefficient in Layer 3

Specific Yield

Recharge in the 

Hollywood Basin

Recharge in the 

West Coast Basin

Recharge in the

Santa Monica Basin

Recharge in the 

Los Angeles Forebay

Recharge in the Central

Basin Pressure Area

15

20

25

30

35

40

15

20

25

30

35

40

20

25

30

35

40

20

25

30

35

40

15

20

25

30

35

40

15

20

25

30

35

40 0.1 1 10

0.1 1 10

0.1 1 10

15

15

15

15

15

20

25

30

35

40

20

25

30

35

40

20

25

30

35

40

PARAMETER MULTIPLIER

15

20

25

30

35

40

ROOT MEAN SQUARE ERROR, IN FEET 15

20

25

30

35

40

0.1 1 10

Figure 33.—Continued.
Development of a Ground-Water Simulation Model 115

Many parameters were important to model 

calibration in particular areas despite being relatively 

insensitive as measured by the RMSE. For example, as 

described above, vertical leakance (Vcont) in layer 2 in 

the West Coast Basin was important for matching 

vertical water-level gradients at monitoring wells 

Inglewood 1 (2S/14W-28M5-7), Carson-1 

(4S/13W-9H9-12) and Gardena-1 (3S/14W-13J6-8), 

although it did not have a large impact on the total 

RMSE (table 6). 

Results from a sensitivity analysis are affected 

by location of observation wells, parameter definition, 

and boundary conditions. Parameter sensitivity tends to 

increase as the number of observations near that 

parameter increases. Areally extensive parameters tend 

to be more sensitive than more localized parameters 

because more observations can be affected directly. 

Areas within layers that are heavily stressed tend to 

have higher sensitivities. 

Analysis of Regional Ground-Water Budget with 

Ground-Water Simulation Model

 The ground-water simulation just described was 

used to quantify the three-dimensional regional 

ground-water budget. Shown in tables 7 and 8 are 

ground-water budget components for the 30-year 

simulation period from 1971 to 2000 and for the last 

five years of the simulation (1996–2000). The 

components include pumpage, spreading, injection, 

mountain-front and interior recharge, boundary flows, 

and change in storage. The values for these 

components are output directly from the model. For the 

few cells that contain both pumping and injection 

wells, the model outputs a net amount.

As shown in tables 7 and 8, the spreading in the 

Montebello Forebay and injection at the seawater 

barrier projects are the main sources of recharge. Also 

shown is the fact that about 80-percent of total 

pumpage comes from model layer 3, the Upper San 

Pedro aquifer system, and that there has been an 

increase in water in storage over the 30-year simulation 

period in all subareas. Note that there has been a net 

decrease in storage from 1996 to 2000. The small 

differences between simulated total net flow (row G on 

tables 7 and 8) and the simulated total net change in 

storage (row H on tables 7 and 8) are due to rounding 

and the fact that the multi-year averages in tables 7 and 

8 are computed using the rates at a single time step (the 

midpoint) of each stress period to represent the average 

rates during that stress period (it was infeasible to have 

the model save all the flows for all time steps in each 

stress period). 

Average model-calculated lateral flows between 

subareas and vertical flows between the four model 

layers are shown in figure 34. The model results show 

the large horizontal and vertical movements of water 

emanating from the Montebello Forebay. These results 

also indicate relatively small average simulated flows 

of ground water moving across the NIU between the 

Central and West Coast Basins (the simulated average 

net flow over all four model layers is about 

3,200 acre-ft/yr for 1971–2000 and 5,900 acre-ft/yr for 

1996–2000). 

Model-calculated flows between onshore and 

offshore zones provide an indication of seawater 

intrusion. In the West Coast Basin, the modelcomputed average flows are moving onshore in layers 

3 and 4 (representing the Upper and Lower San Pedro 

aquifer systems) and offshore in layers 1 and 2 

(representing the Recent and Lakewood aquifer 

systems)(fig. 34). The simulated average net flow from 

San Pedro Bay to all four model layers is about 

6,100 acre-ft/yr for 1971–2000 and 5,900 acre-ft/yr for 

1996–2000. The simulated average net flow from Santa 

Monica Bay to the West Coast Basin over all four 

model layers is about 1,000 acre-ft/yr for 1971–2000 

and 2,000 acre-ft/yr for 1996–2000. The model 

simulates average flows moving offshore in all model 

layers in the Santa Monica Basin.
116 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Table 7. Average 30-year water budget for historic ground-water simulation, 1971–2000 

Budget item and model layer Montebello 

Forebay

Los Angeles 

Forebay

Whittier 

Area

Central 

Basin

Hollywood

Basin

West Coast 

Basin

Santa Monica 

Basin Total

In acre feet per year

Pumpage

—Layer1 −1,600 0 0 −1,200 0 −90 0 −2890

—Layer2 −8,100 −600 0 −6,500 0 −1,700 −60 −16,960

—Layer3 −33,100 −11,600 −1,300 −108,900 0 −49,400 −5,100 −209,400

—Layer4 −1,400 −9,100 −200 −13,900 0 −1,900 −1,600 −28,100

A. TOTAL −44,200 −21,300 −1,500 −130,500 0 −53,090 −6,760 −257,350

Net flow from adjacent 

inland zones

—Layer1 −132,000 −3,700 −1,400 −900 0 −5,000 0 −143,000

—Layer2 −100 −5,700 −3,700 −11,900 −5,700 −11,900 −10,600 −49,600

—Layer3 26,200 10,700 1,300 108,500 0 22,200 7,000 175,900

—Layer4 −4,800 8,800 200 11,500 0 −1,400 2,300 16,600

B. TOTAL −110,700 10,100 −3,600 107,200 −5,700 3,900 −1,300 −100

C. Spreading 122,900 0 0 0000 122,900

Injection

—Layer1 0 0 0 400 0 3,000 0 3,400

—Layer2 0 0 0 3,200 0 4,600 0 7,800

—Layer3 0 0 0 1,700 0 21,200 0 22900

—Layer4 0 0 0 0 0 500 0 500

D. TOTAL 0 0 0 5,300 0 29,300 0 34,600

E. Mountain front and 

interior recharge

5,700 7,200 5,100 14,300 5,900 15,600 13,100 66,900

Net flow from ocean and 

adjacent basins

—Layer1 7,200 2,800 0 0 0 −900 0 9,100

—Layer2 6,900 2,200 0 6,900 0 −1,000 −1,600 13,400

—Layer3 6,900 900 0 −1,200 0 6,100 −1,800 10,900

—Layer4 6,200 300 0 2,300 0 2,800 −700 10,900

F. TOTAL 27,200 6,200 0 8,000 0 7,000 −4,100 44,300

G. Total net flow, 

(A+B+C+D+E+F)

900 2,200 0 4,300 200 2,710 940 11,250

Change in storage

—Layer1 740 10 20 2,200 0 1600 0 4570

—Layer2 220 2,100 40 1,900 210 1200 740 6,410

—Layer3 10 30 10 60 0 40 40 190

—Layer4 0 10 0 40 0 30 0 80

H. TOTAL 970 2,150 70 4,200 210 2,870 780 11,250
Development of a Ground-Water Simulation Model 117

Table 8. Average 5-year water budget for historic ground-water simulation, 1996–2000

Budget item and model layer Montebello 

Forebay

Los Angeles 

Forebay

Whittier

Area

Central

Basin

Hollywood

Basin

West Coast

Basin

Santa Monica

Basin Total

In acre-feet per year

Pumpage

—Layer1 −2,200 0 0 −1,100 0 0 0 −3,300

—Layer2 −7,100 −230 0 −4,800 0 −1,100 −70 −13,300

—Layer3 −33,800 −11,400 −20 −107,200 0 −48,000 −2,100 −202,520

—Layer4 −1,700 −9,500 −10 −14,000 0 −2,300 −1,200 −28,710

A. TOTAL −44,800 −21,130 −30 −127,100 0 −51,400 −3,370 −247,830

Net flow from adjacent 

inland zones

—Layer1 −134,800 −3,700 −1,500 −4,000 0 −5,400 0 −149,400

—Layer2 −500 −6,500 −2,900 −11,600 −5,300 −12,100 −8,600 −47,500

—Layer3 27,800 10,500 10 109,700 10 25,600 4,100 177,720

—Layer4 −3,700 9,100 10 12,700 0 −900 2,100 19,310

B. TOTAL −111,200 9,400 −4,380 106,800 −5,290 7,200 −2,400 130

C. Spreading 116,200000000 116,200

Injection

—Layer1 0 0 0 290 0 2,400 0 2,690

—Layer2 0 0 0 3,100 0 3,200 0 6,300

—Layer3 0 0 0 2,000 0 15,100 0 17,100

—Layer4 0 0 0 0 0 540 0 540

D. TOTAL 0 0 0 5,390 0 21,240 0 26,630

E. Mountain front and 

interior recharge

5,300 6,800 4,800 13,500 5,500 14,500 12,300 62,700

Net flow from ocean and 

adjacent basins

—Layer1 6,200 2,800 0 0 0 −1,100 0 7,900

—Layer2 6,000 2,200 0 5,500 0 −900 −1,700 11,100

—Layer3 6,000 900 0 −4,700 0 7,200 −2,000 7,400

—Layer4 5,400 300 0 1,200 0 2,700 −800 8,800

F. TOTAL 23,600 6,200 0 2,000 0 7,900 −4,500 35,200

G. Total net flow,

(A+B+C+D+E+F)

−10,900 1,270 390 590 210 −560 2,030 −6,970

Change in storage

—Layer1 −10,500 −50 −220 0 0 320 0 −10,450

—Layer2 −380 1,300 490 810 210 −720 1,900 3,610

—Layer3 −60 10 −10 −150 10 −40 110 −130

—Layer4 −30 0 −10 −100 0 −40 10 −170

H. TOTAL −10,970 1,260 250 560 220 −480 2,020 −7,140
118 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

San Pedro

Bay

Pacific

Ocean

San Pedro

Bay

Pacific

Ocean

San Pedro

Bay

Pacific

Ocean

 Santa 

Monica

 Bay

 Santa 

Monica

 Bay

 Santa 

Monica

 Bay

 Santa 

Monica

 Bay

San Pedro

Bay

Pacific

Ocean

118°14' 118° 00'

34°

07'

30"

33°

45'

118°14' 118° 00'

34°

07'

30"

33°

45'

118°14' 118° 00'

34°

07'

30"

33°

45'

118°14' 118° 00'

34°

07'

30"

33°

45'

EXPLANATION

1,500

21,100

700

600

2,800

7,200

900

3,700

111,600

20,500

6,500

A 1971–2000

700

2,200

6,900

7,700

500

600

1,600 100

300

500

6,900

100

1000 1,800

300

650

600

111,600

20,500

6,500

3,700

103,900

41,500

11,100

19,200

10,100

3,200

3,500

400 500

300

6,200

17,000

700

600

2,300

200

20

100

500 700

100

300

13,000

-3,000

4,300

-2,100

2,600

1,100

800

500

900

6,900

5,900

1,600

1,800 300

1,400

1,200

100

1,500 700

100

500

10

2,700

103,900

41,500

19,200

11,100

10,100

13,000

- 3,000

4,300

-2,100

2,600

1,100

200

1,200

3,400

64,200

3,500

800

3,200

Whittier

Narrows

Whittier

Narrows

Layer 1

Layer 2

Layer 3

Layer 4

0

0 10 KILOMETERS

10 MILES

0

0 10 KILOMETERS

10 MILES 0

0 10 KILOMETERS

10 MILES

0

0 10 KILOMETERS

10 MILES

 Hollywood 

Basin Los

Angeles

Forebay

Los Angeles 

Forebay Los Angeles Forebay

Montebello

 Forebay

Whittier

Area

Los Angeles

Narrows

Whittier

Narrows

Whittier

Narrows

Los Angeles

Narrows Los Angeles

Narrows

Los

Angeles

Narrows

Hollywood Basin

Los Angeles Forebay

Montebello

 Forebay

Whittier

Area

 Hollywood Basin

Montebello

 Forebay

Whittier

Area

Hollywood Basin

Montebello

 Forebay

Whittier

Area

Unconsolidated deposits

Consolidated rocks

Outside study area

Average simulated horizontal flow and direction

(1971-2000) – In acre-feet per year 6,900

Average simulated vertical flow from overlying

layer (1971-2000) – In acre-feet per year

111,600

Average simulated vertical flow to underlying

layer (1971-2000) – In acre-feet per year

19,200

Santa

Monica

Basin

West Coast

Basin

Central

Basin

Central

 Basin

Central

 Basin

 Pressure

Area

Santa Monica

Basin

West Coast

Basin

Central

Basin

Pressure

Area

Santa Monica

Basin

West Coast

Basin

Pressure

Area

Santa Monica

Basin

West Coast

Basin

Pressure

Area

Orange

County

Orange

County

Orange

County

Orange

County

Figure 34. Average model-simulated inter-zone flows for layers 1–4 for 1971–2000 (A) and 1996–2000 (B), Los Angeles County, California.
Development of a Ground-Water Simulation Model 119

San Pedro

Bay

Pacific

Ocean

San Pedro

Bay

Pacific

Ocean

San Pedro

Bay

Pacific

Ocean

San Pedro

Bay

Pacific

Ocean

 Santa 

Monica

 Bay

 Santa 

Monica

 Bay

 Santa 

Monica

 Bay

2,900

2,900

2,800

6,200

900 25,000

1,100

600

8,300

3,700 110,600

26,100

1200

2,200

6,000

7,200

600

2,900

8,000

2,800

1,600 200

400

300

5,500

100

900 1,800

300

700

1,400 103,700

46,500 21,900

11,300 110,600

26,100

3,700

8,300

600

300 800

300

5,400

17,200

800

900

1,200

3,600

100

400 100

500 600

100

300

14,000

-1,600

4,500

-2,200

2,700

1,000

800

1,000

900

6,000

20

61,500

6,000

1,600

800

2,000 600

2,000

4,700

2,700

400

1,400 700

200

500

14,000

-1,600 -2,200

4,500

1,000

2,700

103,700

46,500

11,300

21,900

8,000

2,900

2,800

1,200

1,100

B 1996 –2000

EXPLANATION

118°14' 118° 00'

34°

07'

30"

33°

45'

118°14' 118° 00'

34°

07'

30"

33°

45'

118°14' 118° 00'

34°

07'

30"

33°

45'

118°14' 118° 00'

34°

07'

30"

33°

45'

 Santa 

Monica

 Bay

Unconsolidated deposits

Consolidated rocks

Outside study area

Average simulated horizontal flow and direction

(1996-2000) – In acre-feet per year 6,900

Average simulated vertical flow from overlying

layer (1996-2000) – In acre-feet per year

26,100

Average simulated vertical flow to underlying

layer (1996-2000) – In acre-feet per year

46,500

0

0 10 KILOMETERS

10 MILES

0

0 10 KILOMETERS

10 MILES 0

0 10 KILOMETERS

10 MILES

0

0 10 KILOMETERS

10 MILES

West Coast

Basin

Santa Monica

Basin

Central

Basin

Los

Angeles

Forebay

Montebello

Forebay

Pressure

Area

Whittier

Area

West Coast

Basin

Santa Monica

Basin Santa Monica

Basin

Layer 1

Layer 2

Layer 3

Layer 4

 Hollywood 

Basin

Central

Basin

Los

Angeles

Forebay

Montebello

Forebay

 Pressure

Area

Whittier

Area

West Coast

Basin

 Hollywood Basin

 Hollywood Basin Hollywood Basin

Central

Basin

Los

Angeles

Forebay

Montebello

Forebay

Pressure

Area

Whittier

Area

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Pressure

Area

Whittier

Area

Whittier

Narrows

Whittier

Narrows

Whittier

Narrows

Whittier

Narrows

Los Angeles

Narrows Los Angeles

Narrows

Los Angeles

Narrows

Los Angeles

Narrows

Orange

County

Orange

County

Orange

County

Orange

County

Figure 34.—Continued.
120 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Model-computed average net flow through the 

Los Angeles Narrows (from the San Fernando Valley) 

through all layers is 6,200 acre-ft/yr for both 

1971–2000 and for 1996–2000 (fig. 34). Modelcomputed average net flow through the Whittier 

Narrows (from the San Gabriel Valley) is 

27,200 acre-ft/yr for 1971–2000 and 23,600 acre-ft/yr 

for 1996–2000. Model-computed average net flow 

from Orange County is 8,000 acre-ft/yr for 1971–2000 

and 2,000 acre-ft/yr for 1996–2000. For these 

computed flows at head-dependent boundaries, the 

total simulated flow for all layers is considered to be a 

reasonable estimate. How the model apportions these 

flows among the layers is probably not significant, as it 

is very dependent on the assumptions used to define the 

boundary head value in each layer. The computed 

flows at the Orange County boundary are similar in 

magnitude to those computed from a three-layer model 

of the Orange County Basin developed by the Orange 

County Water District, which has a specified head 

boundary located about five miles into Los Angeles 

County. In that model, the average simulated flow 

across the County line for the period 1990–99 was 

9,300 acre-ft/yr; the average simulated flow for the 

period 1996–99 was 8,200 acre-ft/yr (Tim Sovich, 

Orange County Water District, oral commun., 2002). 

In addition to these mean simulated flows, it is 

instructive to consider temporal trends. These are 

shown in figure 35. For example, simulated flows 

through the Whittier Narrows vary considerably yearto-year depending on the water levels in the upper part 

of the Montebello Forebay, which are, in turn, mostly a 

function of the amount of spreading. Simulated net 

flows into the model area from Orange County 

generally decrease through the model period, showing 

a significant shift in flow beginning about 1984. The 

average total simulated flow from 1971 to 1983 across 

the Orange County boundary is 14,000 acre-ft/yr. The 

average total simulated flow from 1984 to 2000 is 

3,300 acre-ft/yr. 

Simulated flows from San Pedro Bay into the 

West Coast Basin show a slightly decreasing trend 

during the model period (fig. 35). This is consistent 

with the general rise in water levels in the southern part 

of the West Coast Basin (for example, wells 

4S/13W-21H5 and -23B2 and -30G1 in Appendix VI). 

Note in figure 35 that the model shows small flows to 

the San Pedro Bay in layers 1 and 2, and significantly 

larger flows from the Bay in layers 3 and 4. Simulated 

flows across the NIU from the Central to the West 

Coast Basin were higher in the last 6 years of the 

simulation period. 

Model Sensitivity to Orange County Boundary 

Condition

To test the model sensitivity to the assumed 

time-varying specified head along the Orange County 

boundary, the historical model simulation was rerun 

replacing the time-varying specified-head boundary 

with a specified- flow boundary. This flow boundary 

was specified along the segment of the specified-head 

boundary that runs north-south (figs. 22B, C); the 

north-most segment of the specified head boundary, 

running east-west, was re-specified as no flow. 

Constant flows of 14,000 and 3,300 acre-ft/yr were 

specified for the periods 1971–83 and 1984–2000, 

respectively (see discussion of fig. 35 in previous 

section). Each flow was apportioned by putting 

50 percent in layer 2, 25 percent in layer 3, and 

25 percent in layer 4. Resulting simulated water levels 

for 2000 are shown in figure 36. As can be seen from 

comparing these results with those in figure 31, the 

model results change little except for selected areas 

extending 2–4 model cells from the boundary. Using 

the model to draw conclusions about activities in these 

areas near the boundary—operations of the Alamitos 

Gap Barrier Project, for example—is not appropriate. 

The sensitivity to this boundary condition of 

simulations of potential future scenarios and of 

optimization analyses is discussed later. 

Model Limitations

Areal recharge—mountain-front recharge and 

distributed interior recharge—rates in the model are 

estimated and applied in a simplified manner. An 

important area for additional work would be to develop 

more processed-based, spatially distributed estimates 

of natural recharge. This would require rigorous 

analysis and integration of rainfall/runoff relations, 

infiltration properties, land use (and associated applied 

water), pipeline leakage, unsaturated flow properties, 

and chemical isotope indicators. 
Development of a Ground-Water Simulation Model 121

YEAR

1970 1980 1990 2000

YEAR

1970 1980 1990 2000

Layer 1

Layer 2

Layer 3

Layer 4

Total

EXPLANATION Central Basin to West 

Coast Basin (across 

Newport-Inglewood Uplift)

San Pedro Bay

to West Coast Basin 

Santa Monica Bay South 

to West Coast Basin 

SIMULATED OCEAN INFLOW, IN 

THOUSANDS OF ACRE-FEET PER YEAR

SIMULATED OCEAN INFLOW, IN 

THOUSANDS OF ACRE-FEET PER YEAR

SIMULATED OCEAN INFLOW, IN 

THOUSANDS OF ACRE-FEET PER YEAR

SIMULATED INTER-BASIN FLOW, 

IN THOUSANDS OF ACRE-FEET PER YEAR

Santa Monica Bay North

to Santa Monica Basin

Orange County

to Central Basin 

-10

0

10

20

30

40

Whittier Narrows to 

Montebello Forebay 

-10

0

10

20

30

40

SIMULATED BOUNDARY INFLOW TO MODEL, 

IN THOUSANDS OF ACRE-FEET PER YEAR

Los Angeles Narrows 

to Los Angeles Forebay

-10

0

10

20

30

40

-10

0

10

20

30

40

-10

0

10

20

30

40

-10

0

10

20

30

40

-10

0

10

20

30

40

A

B

C

E

D

F

G

Figure 35. Annual model-simulated flows between zones and from basins outside model area, 1971–2000, Los Angeles County, California.
122 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Model Boundary

Grid Cell

20

0

60

100

60

20

12

50

79

63

110 Santa 84

Monica

Bay

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

San Pedro Bay

Orange County

Los Angeles

 County

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

EXPLANATION

50

130

Dry cells

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

A Layer 1

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Simulated water-level contour - shows simulated water-level 

in feet above sea level. Contour interval 20 feet. 

Measured water-level (in feet above sea level). 

Figure 36. Model-simulated and measured water levels, 2000, with specified flow boundary at Orange County for layers 1–4 of the ground-water simulation 

model: Layer 1, Recent aquifer system (A); Layer 2, Lakewood aquifer system (B); Layer 3, Upper San Pedro aquifer system (C); and Layer 4, Lower San Pedro 

aquifer system (D), Los Angeles County, California.
Development of a Ground-Water Simulation Model 123

50

130

Dry cells

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

Simulated water-level contour - shows simulated water-level 

in feet above sea level. Contour interval 20 feet. 

Measured water-level (in feet above sea level). 

EXPLANATION

Grid Cell

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier Area

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

B Layer 2

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Orange County

Los Angeles

 County

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

200 120

200

40

40

40

80

0

0

0

0

0

0

0

40

40

80

80

80

80

40

40

120

0

0

80

98 81

117

62

106

-26

191

17

-17

0

-3 -27

-24

-27

-12

-22

39

16

-15

-15 -17

0

216

-28

-5

45

Santa

Monica

Bay

San Pedro Bay

Figure 36.—Continued.
124 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Grid Cell

Pacific

Ocean

50

130 Simulated water-level contour - shows simulated water-level 

in feet above sea level. Contour interval 20 feet. 

Measured water-level (in feet above sea level). 

EXPLANATION

0

40

0

-40

-40

-40

40

80

80

80

0

40

40

0

0

0

40

-40

-40

-80

-40

0

0

0

80

80

120

120

80

100

40

120

120

-80

73

1

39

92

136

37

135 -43

-47

-8

61

-34

-35

-56

0

-72 -65

-72

-25 -6

-60

-72

-86 -98

-43

-40

-28

-21

-22

-26

33

-18

-21

-40

7

-80

132

-31 -43

-6

-4

-98

14

-58

Montebello

Forebay Whittier

Area

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Hollywood

 Basin

Sa

M i on ca

Bay

Sa P dro Bay an P dr Bay

0

0246 8 10 KILOMETERS

246 8 10 MILES

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

C Layer 3

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Orange County

Los Angeles

 County

Figure 36.—Continued.
Development of a Ground-Water Simulation Model 125

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Grid Cell

0

0

40

-40

-40

40

-40

80

80

40

40

0

0

0

40

40

-40

-40

-40

0

0 80

120

80

40

120

120

77

137

65

81

-23

-23

-41

-24-25

0

-44 -86

-72

-52

-32

-51

0

-9

-22

-51

-42

84

Santa Monica

 Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

 Basin

Whittier

Area

Santa

Monica

Bay

San Pedro Bay

EXPLANATION

50

130

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

D Layer 4

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Orange County

Los Angeles

 County

Simulated water-level contour - shows simulated water-level 

in feet above sea level. Contour interval 20 feet. 

Measured water-level (in feet above sea level). 

Figure 36.—Continued.
126 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Offshore-boundary conditions also are treated in 

a very simplified manner, extrapolating aquifer 

surfaces offshore and applying equivalent freshwater 

heads and conductance values as general-head 

boundaries. Increased understanding of the offshore 

hydrostratigraphy and the location(s) of the 

freshwater/seawater interface(s) are needed to more 

accurately simulate ground-water flow at and near the 

ocean boundaries. 

The eastern boundary with Orange County is 

treated as a time-varying specified-head boundary. In 

fact, the Orange County Basin and the basins 

considered in this report—Central, West Coast, Santa 

Monica, and Hollywood Basins—are part of the same 

geohydrologic system. Coordinated use of this model 

and the model of the Orange County Basin developed 

by the Orange County Water District will help reduce 

geohydrologic uncertainties along the Orange 

County—Los Angeles County boundary. In the future, 

developing an integrated model of the combined 

Orange-Los Angeles County coastal ground-water 

basins may be beneficial. 

The model represents the regional ground-water 

system with four layers. In at least some parts of the 

study area, water levels in the upper and lower parts of 

layer 3 respond differently. This points to the potential 

of subdividing layer 3 into at least two separate layers. 

As is discussed below in the section on particle 

tracking, further subdivision of model layers would be 

necessary to simulate solute transport. 

The model uses annual stress periods for the 

historical simulations. It does not simulate seasonal 

changes in water levels. In some locations (for 

example, wells 4S/12W-28H9, 4S/13W-12K1, and 

USGS monitoring sites La Mirada-1, Long Beach-1, 

and Lakewood-1 in Appendix VI) seasonal water-level 

changes are significant. Incorporating shorter stress 

periods into the model would allow representation of 

these seasonal changes. Note that in the simulations of 

future scenarios and in the optimization analyses 

described later, 6-month stress-periods are used.

The model does not incorporate simulation of 

subsidence, because virtually all measured water levels 

during the simulation period, 1971–2000, were above 

historic low values (fig. 7). However, during the late 

1990s, some seasonal low water levels in the Long 

Beach area (well 4S/12W-28H9 in figure 7) are at or 

just below the historic low levels that occurred around 

1960. To accurately simulate the effects of continuing 

drawdowns in this area would require incorporating the 

Interbed Storage Package for MODFLOW (Leake and 

Prudic, 1988).

The model calibration focused on matching 

water levels at USGS multiple-well monitoring sites 

and a set of long term historical water levels. 

Incorporating additional depth-dependent water-level 

data in areas of current data gaps would reduce model 

uncertainty (figure 23 shows location of USGS 

multiple-well monitoring sites used in model 

calibration). Formal parameter-estimation techniques 

were not used in the calibration of this model. 

Applying such techniques could provide improved 

estimates of parameter values and statistical measures 

of the correlation between parameters. 

APPLICATIONS OF THE GROUND-WATER 

SIMULATION MODEL

Particle Tracking Analyses

The MODFLOW ground-water flow model just 

described was coupled with MODPATH, a particletracking routine developed by the USGS to simulate 

advective transport. Details on the algorithm and 

assumptions in MODPATH are given by Pollock 

(1994). The particle-tracking analysis was used in this 

study to evaluate the historical movement of water 

from the spreading grounds in the Montebello Forebay 

and to estimate the net advective movement of water 

from the coastline and from injection wells during the 

model period. 

MODPATH requires selected MODFLOW input 

data sets and output files, including cell-by-cell flows 

for each time step. Additional required inputs include 

porosity (n), top and bottom elevations of layers, and 

particle-starting locations. Initially, a porosity of 0.25 

was assumed for all model layers. 
Applications of the Ground-Water Simulation Model 127

As noted earlier, tritium data collected as part of 

this study showed the highest tritium value for well 3 at 

Downey-1 monitoring site (3S/12W-9J3) (fig. 18), 

suggesting that this water was recharged near the time 

of peak tritium concentrations in the atmosphere. 

Tritium/helium age dating of samples collected in 1998 

provided an estimated age for water collected at 

Downey-1 well 3 (3S/12W-9J3) of 30 years and for 

water from Downey-1 well 2 (3S/12W-9J2) of 34 years 

(Robert Anders, U.S. Geological Survey, San Diego, 

written commun., 2001). This is consistent with the 

results of Schroeder and others (1993) and Michel and 

Schroeder (1994) showing the highest tritium 

concentration in water delivered from the Colorado 

River occurred in 1967. 

The first particle tracking application consisted 

of placing particles at the tops and bottoms of 

perforations of Downey-1 wells 2 and 3 (both in model 

layer 3) in 1998 and backward tracking the particles to 

their point of entry in the system in the area of the 

spreading grounds. Because the simulation period 

began in October 1970, it was assumed for this analysis 

that prior water levels were constant at the initial 

steady-state conditions. 

Using the initial assumed 0.25 porosity for all 

model layers, backward particle-tracking simulations 

from Downey-1 wells 2 and 3 resulted in computed 

ages of 103 and 54 years, respectively. This is far older 

than the tritium--helium computed ages (34 and 

30 years, respectively). 

This overestimate in age is likely explained by 

the fact that MODPATH uses average hydraulic 

conductivity within each layer to compute advective 

velocities. In reality, most transport probably occurs 

preferentially within high-permeability zones within 

each aquifer system. To truly model this transport 

requires much more detailed vertical discretization—

that is, discretely modeling these higher conductivity 

zones. In the context of the four-layer regional flow 

model, it is possible to crudely estimate the fraction of 

the layer thickness in which most flow is actually 

occurring by artificially reducing the porosity value 

input into the model. This has the same result as 

reducing the aquifer thickness while maintaining the 

same effective aquifer transmissivity (hydraulic 

conductivity times thickness) calibrated for the flow 

model. In order to get rates of advective particle 

movement that are consistent with the tritium/helium 

age estimates, it was necessary to reduce the model 

porosity value for layer 3 to 0.05, which is 20 percent 

of the originally assumed porosity value of 0.25. Flow 

paths of water particles are shown in figure 37. The 

thickness of model layer 3 (the Upper San Pedro 

aquifer system) in cells within the flow paths shown in 

figure 37 ranges from about 570 to 760 ft (fig. 24). This 

implies that high-conductivity zones that dominate 

flow in layer 3 are between 110 and 150 ft in 

cumulative thickness. However, since the actual 

hydraulic gradient prior to 1970 was steeper than is 

simulated in this simplified analysis; at least a small 

part of the artificial reduction, in porosity in the model 

is accounting for this steeper gradient. 

This backward particle-tracking simulation 

indicates that the apparent location of the tritium peak 

(and the tritium/helium age estimates) at the USGS 

Downey-1 well 3 is generally consistent with the 

geohydrologic conceptualization as incorporated into 

the regional flow model, if one assumes that most flow 

within the Upper San Pedro aquifer system (model 

layer 3) occurs within about 20 percent of the total 

aquifer-system thickness. 

The second application of particle tracking 

involved forward-tracking of water from the spreading 

grounds from the time of the tritium peak in water 

imported from the Colorado River, 1967 to 2000, using 

the reduced porosity of 0.05 for layer 3. Particles were 

placed in each of the 24 cells representing spreading 

ponds (25 particles in each cell for a total of 

600 particles). Results shown in figure 38 provide an 

estimate of the extent of advective movement of 

artificial recharge. Most (66 percent, or 396 particles, 

including 34 particles that ended in pumping wells) of 

the recharged particles were in layer 3 by 2000, about 

22 percent (129 particles) were in layer 2, about 

12 percent (73 particles, including 4 that ended in 

pumping wells) were in layer 4, and less than 1 percent 

(2 particles) were in layer 1. 
128 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

B

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

 Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Downey-1

Whittier

Area

Santa

Monica

Bay

San Pedro San Pedro

Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Orange County

Los Angeles

 County

Rio Hondo spreading cell

USGS well

San Gabriel spreading cell

North

Spreading grounds

South

Downey-1 well

Layer 1

Layer 2

Layer 3

Layer 4

0

0 2 4 6 KILOMETERS

1 2 4 6 MILES

EXPLANATION

Particle

path

Figure 37. Model-simulated backward tracking of advective flow paths of water particles from U.S. Geological Survey Downey-1 monitoring site in 

1998 to their time of entry into the simulation model, Los Angeles County, California (A, aerial view; B, cross-sectional view).
Applications of the Ground-Water Simulation Model 129

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Downey-1

Lakewood-1

Whittier

Area

USGS wells

Model-simulated advective flow path

EXPLANATION

Santa

Monica

Bay

San Pedro S Pan edro San Ped o

Bay

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Orange County

Los Angeles

 County

Rio Hondo spreading cell

San Gabriel spreading cell

Figure 38. Model-simulated forward tracking of advective flow paths of water particles from spreading grounds, 1967–2000, Los Angeles County, California.
130 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

The third application of the particle-tracking 

analysis involved the tracking of particles with initial 

starting locations in layer 3 along the coast in the West 

Coast Basin, again using the same parameters, 

including the artificial 0.05 value of porosity in model 

layer 3. The path of particle movement over the model 

period, 1971–2000, is shown in figure 39A. The 

average velocities of the particles over the 30-year 

period ranged from 0.1 to 2.1 ft/d (mean of 0.6 ft/d) 

along the Santa Monica Bay and from 0.1 to 1.0 ft/d 

(mean of 0.5 ft/d) along the San Pedro Bay. Of note in 

figure 39A is the large inland distance traveled by 

particles that originate just north of Redondo Canyon, 

apparently as a result of limited simulated injection in 

layer 3 in that area. Historical data on injection rates at 

individual wells are limited; more accurate estimates of 

the actual amount of water injected in each well in the 

barrier projects is needed to validate the particletracking results in this region.

A fourth and final particle-tracking simulation 

was conducted to estimate how much of the injected 

water moves inland, recharging the West Coast Basin 

aquifers. To conduct this simulation, 10 particles were 

placed in each injection well at the beginning of each 

of the 30 stress periods (a total of 24,497 particles over 

the simulation period; an average of 817 particles per 

stress period). Results show that nearly all particles 

move inland (that is, few move toward the ocean) 

(fig. 39B). About 15 percent of the particles injected 

were eventually captured by pumped wells during the 

simulation period. The simulated 30-year advective 

paths of water injected in 1971 are shown in 

figure 39B.

The particle-tracking analyses provide insight 

into the pathways, travel times, and velocities of water 

spread in the Montebello Forebay, water from offshore, 

and water injected in barrier wells. However, the 

significant limitations of particle tracking must be 

reiterated. First, particle tracking considers only 

advective transport (dispersion is not considered). 

Second, reasonable results from the particle tracking 

can be achieved only if it is assumed that most of the 

flow in the Upper San Pedro aquifer system (model 

layer 3) is transmitted within about 20 percent of the 

total thickness. More rigorous simulation of transport 

of recharge water or of seawater requires a true solutetransport model with more detailed vertical 

discretization. 

Simulation of Future Water-Management 

Scenarios

The ground-water simulation model was used to 

evaluate two possible future water-management 

scenarios being considered by local water managers. 

The inputs used for the scenarios are presented in 

table 9. The two scenarios differ only in that scenario 2 

incorporates increased pumpage in the Central Basin.

These future scenarios were evaluated in the 

following way. Model-simulated water levels for 2000 

(fig. 31) were used as initial conditions. The future 

simulation period was 25 years, 2001–25. Instead of 

the annual stress periods used in the historical transient 

simulations described above, 6-month model stress 

periods were used. Specified heads along the Orange 

County boundary initially were set to vary seasonally, 

based on average high (October–March) and low 

(April–September) water levels during recent years 

(1996–2000). The same total annual values of interior 

areal recharge and mountain-front recharge used for 

1971–95 in the historical simulation were used, but 

were prorated into the 6-month stress periods on the 

basis of the fraction of total annual precipitation during 

each 6-month period. Six-month values of historical 

spreading for 1971–95 were used for the future 

simulations. 

Injection rates were set as follows. Injection at 

the West Coast Basin Barrier Project was set equal to 

the 2000 rate of 18,700 acre-ft/yr. Injection at the 

Dominguez Gap Barrier Project was set equal to the 

2000 rate of 6000 acre-ft/yr plus an additional 2,900 

from a first set of planned new wells in April 2002 and 

4,350 from a second set of planned new wells in 

October 2003 (an ultimate total of 13,250 acre-ft/yr). 

Injection at the Alamitos Gap Barrier Project was set 

equal to the 2000 rate of 5,800 acre-ft/yr with an 

increase of 1,300 acre-ft/yr from planned new wells 

starting in April 2002 (an ultimate total of 

7,000 acre-ft/yr). Operation of a newly installed 

desalination well in the Torrance area was 

incorporated, pumping at a constant rate of 

3,045 acre-ft/yr from layer 3. In future scenario 1, 

pumping rates were set equal to the average 6-month 

rates over the period 1997-2000. In future scenario 2, 

pumpage from all wells in the Central Basin (with the 

exception of wells operated by the City of Los 

Angeles) were increased 25 percent from the 

1997–2000 rates over the simulation period (in 

5-percent increments every 5 years) (table 9). 
Applications of the Ground-Water Simulation Model 131

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

0

0246 8 10 KILOMETERS

246 8 10 MILES

Model-simulated advective flow path

Particle starting locations at coastline

EXPLANATION

San Pedro San Pedro

Bay

Santa

Monica

Bay

A

Whittier

Narrows

Redondo Canyon

Los Angeles

Narrows

Pressure

Area

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Orange County

Los Angeles

 County

Figure 39. Model-simulated advective flow paths of water particles from coastline, Layer 3, 1971–2000 (A) and from injection wells, 1971–2000 (B), Los 

Angeles County, California.
132 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

0

0246 8 10 KILOMETERS

246 8 10 MILES

Model-simulated advective flow path

Particle starting locations at injection wells

Redondo Canyon

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Orange County

Los Angeles

 County

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

EXPLANATION

B

Pacific

Ocean

Santa

Monica

Bay

San Pedro San Pedro

Bay

Figure 39.—Continued.
Applications of the Ground-Water Simulation Model 133

Table 9. Inputs used for future model scenarios (2001–25) 

Model input Scenario 1 Scenario 2

Recharge 

(spreading, 

mountain front, 

and interior)

1971–95 values 

(divided into 6 month stress 

periods)

Same as scenario 1

Injection West Coast Basin Barrier 

Project:

Same as scenario 1

—2000 rate 

(18,700 acre-ft/yr)

Dominguez Gap Barrier 

Project:

Same as scenario 1

—Oct. 2000– March 

2002: 2000 rate 

(6,000 acre-ft/yr)

—April 2002–Sept, 2003: 

additional 2,900 

acre-ft/yr

—Oct. 2003–Sept, 2025: 

additional 4,350 

acre-ft/yr

Alamitos Gap Barrier 

Project: 

Same as scenario 1

—Oct. 2000– March 

2002: 2000 rate 

(5,800 acre-ft/yr)

—April 2002–Sept, 2025: 

additional 1,300 

acre-ft/yr

Desalination pumping 3,045 acre-ft/yr Same as scenario 1

Pumpage Average 1997–2000 

6-month values

Increase Central Basin pumpage (excluding City of Los Angeles 

wells) 25-percent over future simulation periods (in 5-percent 

increments every 5 years)
134 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

The values for the flow components in tables 10

and 11 are output directly from the model. As noted for 

tables 7 and 8, the model outputs a net pumpage or 

injection for the small number of cells that contain both 

pumping and injection wells.

Shown in figures 40 and 41 are the simulated 

drawdowns for layer 3 and hydrographs for selected 

wells for 2001 to 2025 for scenario 1 and scenario 2 (in 

figs. 40A and 41A positive drawdowns represent water 

level declines and negative drawdowns represent water 

level rises). For scenario 1, water levels throughout 

most of the model area are generally constant or 

slightly increasing throughout the 25-year simulation 

period. (Note that the apparent water-level declines in 

the southeast part of the Central Basin Pressure Area 

shown in figure 40A reflect seasonal drawdown from 

the average annual 2000 water levels used as initial 

conditions; long term trends can be seen in the 

hydrographs shown in figure 40B). The simulation 

results for scenario 2 (fig. 41) show water levels 

decreasing by 25 to 50 ft in much of the Central Basin. 

Simulation results for scenario 1 indicate that there is 

an average increase in storage in the onshore areas of 

about 8,000 acre-ft/yr (table 10). For scenario 2, there 

is an average decrease in storage of about 

9,000 acre-ft/yr (table 11). 

Average model-calculated ground-water flows 

laterally between basins and subareas and vertically 

between the four model layers for future scenarios 1 

and 2 are shown in figures 42 and 43. The simulated 

flows for future scenario 1 (fig. 42) are generally 

similar to those for 30-year historical simulation 

(fig. 34A). The increased pumpage in the Central Basin 

in scenario 2 results in additional water being drawn 

from the Whittier Narrows boundary to the Montebello 

forebay and from the Orange County Boundary into the 

Central Basin Pressure area. Note that there also is a 

very slight increase in flows from offshore into the 

West Coast Basin (figs. 42, 43).

An important issue in testing future scenarios is 

the assumption made about the Orange County 

boundary condition. As with the historical simulations, 

the two future scenarios were re-run with a constant 

flow specified along the Orange County boundary. A 

flow of 3,700 acre-ft/yr, prorated 50 percent to layer 2 

and 25 percent each to layers 3 and 4, was applied. The 

results for scenario 1 with the constant-flow boundary, 

which are shown in figure 44, do not differ greatly 

from the results for the specified head-case shown in 

figure 40. In contrast, the results for scenario 2 with the 

constant-flow Orange County boundary, which are 

shown in figure 45, show more drawdown throughout 

the Central Basin than the results for the specified-head 

case shown in figure 41. 

These potential future water-management 

strategies are just two of many possible scenarios that 

the model can be used to evaluate. Other scenarios 

could incorporate alternative assumptions regarding 

future water demand, availability of surface-water 

supplies, development of new projects, and the impacts 

of climatic variability.
Applications of the Ground-Water Simulation Model 135

Table 10. Average water budget for future scenario 1, 2001–2025

Budget item and model layer Montebello 

Forebay

Los Angeles 

Forebay

Whittier 

Area

Central

Basin

Hollywood

Basin

West Coast

Basin

Santa Monica

Basin Total

In acre-feet per year

Pumpage

—Layer1 −2,500 0 0 −2,100 0 0 0 −4,600

—Layer2 −6,600 −240 0 −4,300 0 −1,200 −60 −12,400

—Layer3 −33,800 −11,500 −20 −108,000 0 −51,200 −1,800 −206,320

—Layer4 −1,800 −9,600 −10 −16,400 0 −2,400 −1,200 −31,410

A. TOTAL −44,700 −21,340 −30 −130,800 0 −54,800 −3,060 −254,730

Net flow from adjacent 

inland zones

—Layer1 −131,700 −3,700 −1,400 −3,700 0 −5,200 0 −145,700

—Layer2 −1,300 −7,800 −3,600 −10,100 −5,500 −14,000 −10,100 −52,400

—Layer3 27,200 10,700 30 109,600 0 25,100 4,200 176,830

—Layer4 −4,100 9,200 10 14,200 0 -500 2,300 21,110

B. TOTAL −109,900 8,400 −4,960 110,000 −5,500 5,400 −3,600 −160

C. Spreading 124,300 0 0 0 0 0 0 124,300

Injection

—Layer1 0 0 0 400 0 3,200 0 3,600

—Layer2 0 0 0 3,800 0 5,900 0 9,700

—Layer3 0 0 0 2,300 0 20,400 0 22,700

—Layer4 0 0 0 0 0 500 0 500

D. TOTAL 0 0 0 6,500 0 30,000 0 36,500

E. Mountain front and 

interior recharge

5,600 7,400 5,200 14,500 6,000 15,700 13,300 67,700

Net flow from ocean and 

adjacent basins

—Layer1 6,800 2,800 0 0 0 −1,600 0 8,000

—Layer2 6,600 2,200 0 3,600 0 −1,000 −1,800 9,600

—Layer3 6,600 900 0 −4,100 0 5,700 −2,400 6,700

—Layer4 5,900 300 0 2,300 0 2,400 −1,100 9,800

F. TOTAL 25,900 6,200 0 1,800 0 5,500 −5,300 34,100

G. Total net flow 

(A+B+C+D+E+F)

1,200 660 210 2,000 500 1,800 1,340 7,710

Change in storage

—Layer1 1,300 10 30 -20 0 1,200 0 2,520

—Layer2 60 510 160 2,000 510 670 1,400 5,310

—Layer3 10 0 10 −170 0 60 10 -80

—Layer4 0 0 0 80 0 20 0 100

H. TOTAL 1,370 520 200 1,890 510 1,950 1,410 7,850
136 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Table 11. Average water budget for future scenario 2, 2001–2025

Budget item and model layer Montebello 

Forebay

Los Angeles 

Forebay

Whittier 

Area

Central 

Basin

Hollywood

Basin

West Coast

Basin

Santa Monica

Basin Total

In acre-feet per year

Pumpage

—Layer1 −2,900 0 0 −2,400 0 0 0 −5,300

—Layer2 −7,800 −280 0 −5,000 0 −1,200 −60 −14,340

—Layer3 −39,700 −13,600 −20 −126,900 0 −51,200 −1,800 −233,220

—Layer4 −2,200 −11,200 −20 −19,300 0 −2,400 −1,200 −36,320

A. TOTAL −52,600 −25,080 −40 −153,600 0 −54,800 −3,060 −289,180

Net flow from adjacent 

inland zones

—Layer1 −135,900 −3,700 −1,400 −7,200 0 −6,000 0 −154,200

—Layer2 −1,500 −10,400 −3,700 −15,400 −5,700 −14,900 −10,300 −61,900

—Layer3 32,000 12,700 20 120,500 0 24,500 4,200 193,920

—Layer4 −4,700 10,900 20 14,400 0 −700 2,200 22,120

B. TOTAL −110,100 9,500 −5,060 112,300 −5,700 2,900 −3,900 −60

C. Spreading 124,300000000 124,300

Injection

—Layer1 0 0 0 400 0 3,200 0 3,600

—Layer2 0 0 0 3,800 0 5,900 0 9,700

—Layer3 0 0 0 2,300 0 20,400 0 22,700

—Layer4 0 0 0 0 0 500 0 500

D. TOTAL 0 0 0 6,500 0 30,000 0 36,500

E. Mountain front and 

interior recharge

5,600 7,400 5,200 14,500 6,000 15,700 13,300 67,700

Net flow from ocean and 

adjacent basins

—Layer1 8,000 2,800 0 0 0 −1,500 0 9,300

—Layer2 7,700 2,200 0 4,900 0 -900 −1,700 12,200

—Layer3 7,700 900 0 3,900 0 6,300 −2,400 16,400

—Layer4 6,900 300 0 4,900 0 2,600 −1,000 13,700

F. TOTAL 30,300 6,200 0 13,700 0 6,500 −5,100 51,600

G. Total net flow 

(A+B+C+D+E+F)

−2,500 −1,980 100 −6,600 300 300 1,240 −9,140

Change in storage

—Layer1 −2,200 −10 −20 −3,900 0 520 0 −5,610

—Layer2 −250 −2,000 40 −2,500 280 −240 1,200 −3,470

—Layer3 −20 −30 0 −200 0 40 10 −200

—Layer4 −10 −10 0 20 0 −10 0 −10

H. TOTAL −2,480 −2,050 20 −6,580 280 310 1,210 −9,290
Applications of the Ground-Water Simulation Model 137

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay Montebello

Forebay

Hollywood

Basin

Whittier

Area

EXPLANATION

130 Simulated drawdown 2001-2025 in model layer 3. 

 Countour interval 5 feet. (Note: negative drawdowns 

 represent water-level rises)

A

Santa

Monica

Bay

San Pedro San Ped o

Bay

Whittier

Narrows

Redondo Canyon

Los Angeles

Narrows

Pressure

Area

33° 40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Orange County

Los Angeles

 County

20

20

20

10

-10

10

10

0

0

20

40

25

25

-10

-10

-10

-15

-15

-15

-20

-20

0

0

0

0

0

0

5

5

-5

-5

-5

5

5

5

-5

-5

-5

15

15

Figure 40. Model-simulated drawdowns, layer 3 (A) and selected model-simulated hydrographs (B) for future scenario 1, 2001–25, Los Angeles County, 

California.
138 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Los Angeles Forebay

USGS

3S/14W13J5-8 Gardena-1

970, 445, 345, 120 31, 32

2S/13W-17F1-5 Los Angeles-1 

1370, 1100, 940, 660, 370 19, 35

2S/12W-26D9-14 Rio Hondo-1 

1110, 910, 710, 430, 280, 140 22, 52

4S/13W-1N3-8 Long Beach-2 

990, 740, 470, 300, 180, 115 39, 42

3S/13W-8J1-4 Willowbrook-1 

885, 500, 360, 200 29, 36

4S/13W-28A3-7 Wilmington-1 

915, 780, 550, 225,120 46, 37

West Coast Basin

USGS

Central Basin

USGS

West Coast Basin

USGS

Central Basin

USGS

Montebello Forebay

USGS

1996 2006 2026 1996 2016 2006 2026 2016

1996 2006 2026 1996 2016 2006 2026 2016

-25

-50

-75

75

50

0

25

-25

-50

-75

0

25

-100

-125

-25

-50

-75

0

25

-100

-125

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

150

50

25

0

125

75

100

YEAR

WATER LEVEL, IN FEET ABOVE SEA LEVEL

885, 500, 360, 200 Well depths

EXPLANATION

Historical measured 

water levels

Simulated future

water levels

Layer 3

Layer 2

Layer 1

Layer 4

31, 32 Model row and column

B

Figure 40.—Continued.
Applications of the Ground-Water Simulation Model 139

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Santa

Monica

Bay

San

Pedro

Bay

EXPLANATION

Whittier

Narrows

Redondo Canyon

Los Angeles

Narrows

Pressure

Area

33°40'

50'

34° 00'

118° 30' 20' 10' 118° 00'

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

Orange County

Los Angeles

 County

130 Simulated drawdown 2001-2025 in model layer 3. 

Countour interval 5 feet. (Note: negative drawdowns 

 represent water-level rises)

A

20

25

50

35

30

15

10

20

0

0

25

55

55 5

10

0

-10

-10

-10

-10

-15

-15

35

45

35

35

40

35

25

25

-5

-5

 5

 15

0

10

10

25

40

40

40

55

25

75

10

0

40

5

40

45

-5

-5

5

Figure 41. Model-simulated drawdowns, layer 3(A) and selected model-simulated hydrographs (B) for future scenario 2, 2001–25, Los Angeles County, 

California.
140 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Los Angeles Forebay 

USGS

3S/14W-13J5-8 Gardena-1 

970, 445, 345, 120 31, 32

2S/13W-17F1-5 Los Angeles-1 

1370, 1100, 940, 660, 370 19, 35

2S/12W-26D9-14 Rio Hondo-1 

1110, 910, 710, 430, 280, 140 22, 52

4S/13W-1N3-8 Long-Beach-2 

990, 740, 470, 300, 180, 115 39, 42

3S/13W-8J1-4 Willowbrook-1 

885, 500, 360, 200 29, 36

4S/13W-28A3-7 Wilmington-1

915, 780, 550, 225,120 46, 37

West Coast Basin

USGS

Central Basin USGS

West Coast Basin 

USGS

Central Basin 

USGS

Montebello Forebay

USGS

EXPLANATION

Historical measured 

water levels

Simulated future

water levels

885, 500, 360, 200 Well depths

1996 2006 2026 1996 2016 2006 2026 2016

1996 2006 2026 1996 2016 2006 2026 2016

-25

-50

-75

75

50

0

25

-25

-50

-75

0

25

-100

-125

-25

-50

-75

0

25

-100

-125

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

150

50

25

0

125

75

100

YEAR YEAR

WATER LEVEL, IN FEET

ABOVE SEA LEVEL

WATER LEVEL, IN FEET

ABOVE SEA LEVEL

WATER LEVEL, IN FEET

ABOVE SEA LEVEL

31, 32 Model row and column

B

Layer 3

Layer 2

Layer 1

Layer 4

Figure 41.—Continued.
Applications of the Ground-Water Simulation Model 141

San Pedro

Bay

Pacific

Ocean

San Pedro

Bay

Pacific

Ocean

San Pedro

Bay

Pacific

Ocean

 Santa 

Monica

 Bay

 Santa 

Monica

 Bay

 Santa 

Monica

 Bay

 Santa 

Monica

 Bay

San Pedro

Bay

Pacific

Ocean

118°14' 118° 00'

34°

07'

30"

33°

45'

118° 14' 118° 00'

34°

07'

30"

33°

45'

34°

07'

30"

33°

45'

34°

07'

30"

33°

45'

118° 14' 118° 00' 118° 14' 118° 00'

EXPLANATION

Unconsolidated deposits

Consolidated rocks

Outside study area

1,100

22,800

800

2,800

6,800

1600

3,700

6,300

600 109,600

25,400

1,000

2,200

6,600

7,500

600

600

1,800 300

300

600

3,600

200

1000 2,000

400

2,200

500

Average simulated horizontal flow and direction

(2001-25) – In acre-feet per year 1,000

109,600

25,400

6,300

3,700

Average simulated vertical flow from overlying

layer (2001-25) – In acre-feet per year

111,600

103,200

Average simulated vertical flow to underlying

layer (2001-25) – In acre-feet per year

19,200

46,000

11,800

21,600

9,200

2,800

3,300

400 600

300

5,900

17,400

1,100

1,000

2,300

600

200

40

500 600

100

400

13,800

-900

4,800

-1,700

3,200

900

1,000

900

900

6,600

5,000

1,400

2,400 900

2,300

4,100

600

1,400 700

200

400

60

2,600

103,200

46,000

21,600

11,800

9,200

13,800

- 900

4,800

-1,700

3,200

900

700

1,100

3,400

61,800

3,300

1000

Layer 1 2,800

Layer 2 Layer 4

Layer 3

0

0 10 KILOMETERS

10 MILES 0

0 10 KILOMETERS

10 MILES

0

0 10 KILOMETERS

0 10 MILES

0 10 KILOMETERS

10 MILES

 Hollywood 

Basin

Los Angeles

Forebay

Montebello

 Forebay

Whittier

Area

Los Angeles

Narrows

Whittier

Narrows

Whittier

Narrows

Whittier

Narrows

Orange

County

Santa

Monica

Basin

West Coast

Basin

Central

Basin

Central

 Basin

Central

 Basin

Los Angeles Forebay

Los Angeles Forebay

Pressure

Area

Los Angeles

Narrows

Los Angeles

Narrows

Los Angeles

Narrows

Santa Monica

Basin

West Coast

Basin

Hollywood Basin

Hollywood Basin

Central

Basin

Los Angeles 

Forebay

Montebello

 Forebay

Pressure

Area

Whittier

Area

Santa Monica

 Basin

West Coast

Basin

Montebello

 Forebay

Pressure

Area

Whittier

Area

Santa Monica

Basin

West Coast

Basin

Hollywood Basin

Montebello

Forebay

Pressure

Area

Whittier

Area

Figure 42. Average model-simulated inter-zone flows for layers 1–4 for future scenario 1, 2001–25, Los Angeles County, California.
142 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

EXPLANATION

Unconsolidated deposits

Consolidated rocks

Outside study area

300

18,200

700

2,800

8,000

1,500

3,700

6,200

700 118,500

25,100

500

2,200

7,700

7,700

500

700

1,800 300

400

600

4,900

300

1000 400 2,000

2,200

300

Average simulated horizontal flow and direction

(2000-25) – In acre-feet per year 6,900

118,500

25,100

6,200

3,700

Average simulated vertical flow from overlying

layer (2000-25) – In acre-feet per year

1,000

112,300

Average simulated vertical flow to underlying

layer (2000-25) – In acre-feet per year

9,900

51,800

14,200

21,900

9,300

3,000

3,400

400 200

300

6,900

18,400

1,000

1,000

4,900

600

300

0

500 700

200

400

14,000

-1,500

5,800

-1,500

3,300

1,000

1000

200

900

7,700

5,400

1,500

2,400 900

2,300

3,900

1,500 700

500

100

3,100

112,300

51,900

21,900

14,200

9,300

14,000

- 1,500

5,800

-1,500

3,300

1,000

900

1,200

4,000

65,900

3,400

1000

3,000

200

700

0

0 10 KILOMETERS

10 MILES

0

0 10 KILOMETERS

10 MILES

0

0 10 KILOMETERS

10 MILES

0

0 10 KILOMETERS

10 MILES

Layer 1

Layer 2 Layer 4

Layer 3

118° 14' 118° 00'

34°

07'

30"

33°

45'

118° 14' 118° 00'

34°

07'

30"

33°

45'

34°

07'

30"

33°

45'

34°

07'

30"

33°

45'

118° 14' 118° 00' 118° 14' 118° 00'

San Pedro

Bay

Pacific

Ocean

San Pedro

Bay

Pacific

Ocean

San Pedro

Bay

Pacific

Ocean

 Santa 

Monica

 Bay

 Santa 

Monica

 Bay

 Santa 

Monica

 Bay

 Santa 

Monica

 Bay

San Pedro

Bay

Pacific

Ocean

Santa

Monica

Basin

West Coast

Basin

 Hollywood 

Basin

Central

Basin

Central

 Basin

Central

 Basin

Los

Angeles

Forebay

Los Angeles

Forebay

Montebello

 Forebay

Pressure

Area

Whittier

Area

Santa Monica

Basin

West Coast

Basin

Hollywood Basin

Central

Basin

Los Angeles

Forebay

Montebello

 Forebay

Pressure

Area

Whittier

Area

Santa Monica

Basin

West Coast

Basin

 Hollywood 

Basin

Montebello

 Forebay

Pressure

Area

Whittier

Area

Santa Monica

Basin

West Coast

Basin

Pressure

Area

Whittier

Area

Los Angeles

Narrows

Whittier

Narrows

Whittier

Narrows

Los Angeles

Forebay

Montebello

 Forebay

Whittier

Narrows

Los Angeles

Narrows

Hollywood Basin Los Angeles

Narrows Los Angeles

Narrows

Whittier

Narrows

Figure 43. Average model-simulated inter-zone flows for layers 1–4 for future scenario 2, 2001–25, Los Angeles County, California.
Applications of the Ground-Water Simulation Model 143

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

A

Santa

Monica

Bay

Sa

Bay

EXPLANATION

Orange County

Los Angeles County

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

130 Simulated drawdown 2001-2025 in model layer 3. 

Countour interval 5 feet. (Note: negative drawdowns 

 represent water-level rises)

33°

40'

50'

34°

00'

118° 30' 20' 10' 118° 00'

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

10 10

25

-10

-10 -10

-10

-10

0

0

0

40

25

-10

-10

-10

-15

-1

5

-15-20

-25

0

0

-5

-5

-5

-5

-5

5

-5

-5

5

5

5

-5

-5

-5

15

-15

15

-15

15

15

Figure 44. Model-simulated drawdowns, layer 3 (A) and selected model-simulated hydrographs (B) for future scenario 1 with constant flow at the Orange 

County boundary, 2001–25.
144 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Los Angeles Forebay

USGS

3S/14W13J5-8 Gardena-1

970, 445, 345, 120 31, 32

2S/13W-17F1-5 Los Angeles-1 

1370, 1100, 940, 660, 370 19, 35

2S/12W-26D9-14 Rio Hondo-1 

1110, 910, 710, 430, 280, 140 22, 52

4S/13W-1N3-8 Long Beach-2 

990, 740, 470, 300, 180, 115 39, 42

3S/13W-8J1-4 Willowbrook-1 

885, 500, 360, 200 29, 36

4S/13W-28A3-7 Wilmington-1 

915, 780, 550, 225,120 46, 37

West Coast Basin

USGS

Central Basin

USGS

West Coast Basin

USGS

Central Basin

USGS

Montebello Forebay

USGS

1996 2006 2026 1996 2016 2006 2026 2016

1996 2006 2026 1996 2016 2006 2026 2016

-25

-50

-75

75

50

0

25

-25

-50

-75

0

25

-100

-125

-25

-50

-75

0

25

-100

-125

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

150

50

25

0

125

75

100

YEAR

WATER LEVEL, IN FEET ABOVE SEA LEVEL

885, 500, 360, 200 Well depths

EXPLANATION

Historical measured 

water levels

Simulated future

water levels

Layer 3

Layer 2

Layer 1

Layer 4

31, 32 Model row and column

B

Figure 44.—Continued.
Applications of the Ground-Water Simulation Model 145

0

0246 8 10 KILOMETERS

246 8 10 MILES

Pacific

Ocean

Santa Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

Hollywood

Basin

Whittier

Area

Santa

Monica

Bay

San

Pedro

Bay

EXPLANATION

A

Orange County

Los Angeles County

Whittier

Narrows

Los Angeles

Narrows

Pressure

Area

33°

40'

50'

34°

00'

118° 30' 20' 10' 118° 00'

R16W R15W R14W R13W R12W R11W

T1S T2S T3S T4S T5S

130 Simulated drawdown 2001-2025 in model layer 3. 

Countour interval 5 feet. (Note: negative drawdowns 

 represent water-level rises)

20

25

25

25

50

50

60

65

65

70

75

50 55

55

55

15

15

0

0

75

70

0

-10

10

-10

-15

30

30

45

35

35

35

30

30

30

35

35

25

20

20 -5

-5

5

15

0

60 75

45

45

85

10

0

40

5

40

-5

-5

5 5

-5

Figure 45. Model-simulated drawdowns, layer 3 (A) and selected model-simulated hydrographs (B) for future scenario 2 with constant flow at the Orange 

County boundary, 2001–25.
146 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Layer 3

Layer 2

Layer 1

Layer 4

EXPLANATION

Historical measured 

water levels

Simulated future

water levels

Los Angeles Forebay

USGS

3S/14W-13J5-8 Gardena-1 

970, 445, 345, 120 31, 32

2S/13W-17F1-5 Los Angeles-1 

1370, 1100, 940, 660, 370 19, 35

2S/12W-26D9-14 Rio Hondo-1 

1110, 910, 710, 430, 280, 140

22, 52

4S/13W-1N3-8 Long Beach-2

990, 740, 470, 300,

180 115 39, 42

 3S/13W-8J1-4 Willowbrook-1 

885, 500, 360, 200 29, 36

4S/13W-28A3-7 Wilmington-1 

915, 780, 550, 225,120 46, 37

West Coast Basin

USGS

Central Basin USGS

West Coast Basin

USGS

Central Basin

USGS

Montebello Forebay

USGS

1996 2006 2026 1996 2016 2006 2026 2016

1996 2006 2026 1996 2016 2006 2026 2016

-25

-50

-75

75

50

0

25

-25

-50

-75

0

25

-100

-125

-25

-50

-75

0

25

-100

-125

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

150

50

25

0

125

75

100

YEAR YEAR

WATER LEVEL, IN FEET

ABOVE SEA LEVEL

WATER LEVEL, IN FEET

ABOVE SEA LEVEL

WATER LEVEL, IN FEET

ABOVE SEA LEVEL

885, 500, 360, 200 Well depths

31, 32 Model row and column

B

Figure 45.—Continued.
Simulation-Optimization Analysis 147

SIMULATION-OPTIMIZATION ANALYSIS

The simulation model was coupled with 

mathematical optimization algorithms to identify leastcost solutions for improving control of seawater 

intrusion. Initial development of simulationoptimization methods for ground-water management 

was done by Bredehoeft and Young (1970), Deninger 

(1970), Maddock (1972), and Aguado and Remson 

(1974). Literature reviews of simulation-optimization 

research can be found in Gorelick (1983), Yeh (1992), 

Wagner (1995), and Ahfeld and Mulligan (2000). 

Specific applications that utilize optimization methods 

to address issues of seawater intrusion include Shamir 

and others (1984), Willis and Finney (1988), Reichard 

(1995), Nishikawa (1998), Emch and Yeh (1998), 

Chang and others (2000), and Gordon and others 

(2001). 

The base case optimization analysis utilizes 

future scenario 1 presented in the previous section. 

Model- simulated 2025 water levels in layer 3 (Upper 

San Pedro aquifer system) for scenario 1 are shown in 

figure 46. Note that simulated water levels are below 

sea level. The goal of the analysis is to determine the 

most cost effective way to raise water levels along the 

coast, either by increasing injection or reducing 

pumpage through in-lieu delivery of surface water, so 

as to better control seawater intrusion. Sensitivity to 

several factors—restrictiveness of water-level 

constraints, cost structures, and assumed future 

scenario—is evaluated.

Shown in figure 46 are locations of injection in 

cells where additional injection is considered, in lieu 

cells where in lieu delivery of surface water is 

considered (based on information provided by 

WRDSC), and control cells where water-level 

constraints are imposed. 
148 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Pacific

Ocean

11

13

1

12

17

16

8

1 6

4 3

5

10

18

9

15

14

9

19

0

0246 8 10 KILOMETERS

246 8 10 MILES

50

90

70

20

-20 -30

-40

-40

-50

-50

-40

-30

-30

-20

-20

10

-60 -50

20

20

0

-10

-40

-40

-40

30

40 -10

 10

 10

 20

-20

10

-30

20

Palos

 Verdes

 Hills

Long

Beach

Lakewood

Santa

Monica

Basin

West Coast

Basin

Central

Basin

Los Angeles

Forebay

Montebello

Forebay

In-lieu cells

Control cells

EXPLANATION

A

B

C

D

E

F

G

H

I

K

L

J

Injection cells

Simulated 2025 water levels 

 in layer 3, in feet, for 

 future scenario 1.

A

33°

40'

50'

34°

00'

R15W R14W R13W R12W

T2S T3S T4S T5S

20' 118° 10'

Dominguez Gap 

Barrier Project

West

Coast

Basin

Barrier

Project

Figure 46. In-lieu and injection cells for the ground-water simulation model-optimization analysis, Los Angeles County, California.
Simulation-Optimization Analysis 149

The optimization problem is the following:

Minimize: 

(1)

subject to:

(2)

 (3)

 (4)

 (5)

 (6)

 (7)

where: 

cil = cost of water for in-lieu delivery

($168 per acre-ft for base case);

Ilit = in-lieu delivery at location i in time 

period t;

cinj = cost for injection water 

($528 per acre-ft for base case);

cil Ilit ( ) ⋅ cinj Injjt ( ) ⋅

j = 1

J

+ ∑

i = 1

I

∑

t = 1

T

∑

hkt hko = dukt + +

τ = 1

t

∑ αiτkt Ilit ( ) ⋅

i = 1

I

∑ βjτkt Injit ( ) ⋅

j = 1

J

+ ∑ t = 1, T

1 ⁄ T hkt Hmin - avg ≥ k = 1, K

t = 1

T

⋅ ∑

hkt hmin > k = 1, K

hkt hmax < k = 1, K

Ilit Il maxj < – i = 1, I

Injjt Inj maxj < – j = 1, J

Injjt = additional injection at injection cell j in 

time period t;

hkt = head at control location k in time 

period t;

hk0 = head at control location k in time 

step 0;

dukt = drawdown at control location k in time 

step t due to initial and boundary 

conditions and unmanaged stresses;

αiτkt = water-level response at control 

location k at time step t resulting from 

unit in-lieu delivery to location i at time 

τ;

βjτkt = water-level response at control 

location k at time step t resulting from 

unit injection at location j at time τ;

Hmin-avg = lower bound on average water level at 

all control locations (set at 0 ft for base 

case);

hmin = lower bound on water level at control 

locations during each stress period 

(−30 ft);

hmax = upper bound for water level at control 

locations during each stress period 

(30 ft);

Il-maxi = upper bound on in-lieu delivery for 

location i (based on average October–

March, 1997–2000, pumping at that 

location);

Inj-maxj = upper bound on additional injection at 

injection location j (set at 

7,200 acre-ft/yr for all cells);

T = management period (fifty 

6-month periods);

I = in-lieu locations (locations where 

ground-water pumpage can be replaced 

by delivery of surface water) (19);

J = injection locations (12); and

K = water-level control locations (23).
150 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

The objective function of the model, equation 4, 

is to minimize the undiscounted sum of the water costs 

of in lieu delivery (Il) and additional injection (Inj). 

Any additional operational or capital costs are not 

considered. The current (2002) costs for injection (cinj) 

and in-lieu (cil) water, as reported by WRDSC, are 

$528/acre-ft and $168/acre-ft, respectively. The costs 

differ because water delivered for injection must be 

non-interruptible and the in-lieu costs incorporate the 

cost savings resulting from reduced pumpage. The 

implications of this cost differential are explored in the 

sensitivity analysis. 

 Equation 5 incorporates the hydraulics of the 

ground-water flow system. Water levels at control 

location k at time t (hkt) are a function of the initial 

water levels at that location (hk0), unmanaged 

drawdown (dukt), and the sums of all in-lieu deliveries 

(Ilit) and injections (Injit) up through time t multiplied 

by their appropriate response coefficients (αiτkt and 

βjτkt). The response coefficients, αiτkt and βjτkt, are 

generated by repeated runs of the simulation model 

using the processing program MODMAN (Greenwald, 

1998). Each simulation run involves applying a unit 

stress (representing injection or reduced pumpage 

resulting from in-lieu delivery) at one of the 31 in-lieu 

and injection cells shown in figure 46. Response 

coefficients are computed by subtracting the simulated 

changes in water levels at the 23 control locations in 

each of the 50 management periods from the 

unmanaged drawdown.

Equations 6–8 represent head constraints at the 

control locations. Equation 6 constrains average water 

levels (averaged over all 50 management periods) to be 

greater than a specified value, Hmin-avg. Constraining 

water levels in this manner allows levels to be below 

Hmin-avg in some periods, as long as this is offset by 

water levels above Hmin-avg in other periods. The 

implicit assumption in applying this constraint is that 

average water levels are the determining factor in longterm seawater intrusion. For the base-case optimization 

run, the minimum water level allowed at the control 

locations, Hmin-avg, was set equal to 0 (sea level). It is 

recognized that this value is not completely protective 

for seawater intrusion because of the density effects. 

This is addressed in the sensitivity analysis. Equations 

7 and 8 constrain the minimum (hmin) and maximum 

(hmax) water levels allowed at the control locations in 

each period. In the optimization runs described below, 

hmin and hmax are set at –30 ft and 30 ft, respectively.

Equations 9 and 10 represent upper bounds on 

the amount of in-lieu delivery (reduced pumpage) and 

injection at each location. Upper bounds in-lieu 

delivery (Il-max) were determined from 1997–2000 

average winter (October–March) pumpage at the inlieu cells and are listed in table 12. Upper bounds on 

injection (Inj-max) were set at 7,200 acre-ft/yr. 

The optimization model represented by 

equations 4–10 was solved as a linear program using 

the software LINDO (Schrage 1993, 1997). The 

optimization model includes a total of 1,550 decision 

variables and 1,173 constraints (note that equations 

7–10 are represented in LINDO as bounds rather than 

explicit constraints). 

The response matrix approach assumes linear 

conditions. Because unconfined (non-linear) conditions 

are considered in the simulation model, it was 

necessary to solve the optimizations in an iterative 

fashion (Danskin and Freckleton, 1992; Greenwald, 

1998). The iterative solution involves setting the 

calculated pumpage and injection rates from the 

previous optimization solution as fixed rates and 

regenerating the response matrix. The optimization is 

then rerun with the new response matrix, appropriately 

adjusting the bounds on the decision variables. The 

output from the new optimization run is a change in 

rates and objective values from the previous solution. 

The process is repeated until the change in the 

objective function is considered acceptably small (less 

than 0.5 percent). Three to six such iterations were 

required in the optimizations presented below.
Simulation-Optimization Analysis 151

Table 12. Summary of optimization results

[All in-lieu and injection amounts in acre-feet/year; Hmin-avg in feet above sea level; upper bound, maximum rate allowed in optimization; because of 

rounding, all values may not add to totals; *, total cost not listed for runs with varied injection/in-lieu cost ratios]

Optimization run 1 (base) 2 3 4 5 6 7 8 9

Future 

scenario

1 1 1 1 1 1 1 2 2,

constant 

flow 

Hmin-avg 0 5 10 0 0 0 0 0 0

Injection/in-lieu cost ratio 3.3 3.3 3.3 2.5 2 1.5 1 3.3 3.3

In lieu cells Upper bound 

1 2,138 1,026 1,069 681 1,069 1,033 556 0 1,171 1,186

2 3,683 2,910 2,818 2,472 2,838 2,988 2,620 294 3,031 3,142

3 2,108 893 1,181 1,007 859 878 464 0 1,070 1,032

4 3,950 1,456 2,115 1,501 1,417 1,452 790 0 1,623 1,732

5 998 547 643 554 540 542 300 0 670 620

6 1,274 663 806 614 670 663 349 0 816 768

7 1,442 0 288 134 173 144 58 0 173 144

8 1,330 320 533 320 320 320 213 0 453 425

9 1,404 941 960 816 928 843 990 169 1,083 984

10 0 0 0 0 0 0 0 0 0 0

11 3,128 0 0 0 0 0 0 0 0 0

12 1,472 0 0 0 0 0 0 0 0 0

13 1,888 0 0 0 0 0 0 0 0 0

14 2,028 2,000 1,880 1,812 1,988 1,997 1,907 812 1,998 2,007

15 2,530 2,327 2,361 2,362 2,328 2,237 2,100 150 2,276 2,280

16 1,782 0 0 0 0 0 0 0 0 0

17 1,432 0 57 57 0 0 0 0 0 0

18 2,208 2,092 1,822 1,734 2,149 2,122 1,825 354 2,099 2,117

19 3,522 2,756 2,547 1,984 2,719 2,442 2,070 414 2,799 2,781

Total 34,795 17,931 19,080 16,048 17,999 17,661 14,240 2,193 19,263 19,219

Injection cells

A 7,200 0 0 200 0 0 0 0 0 0

B 7,200 0 0 40 0 0 0 0 0 0

C 7,200 0 0 0 0 0 0 0 0 0

D 7,200 0 0 0 0 0 0 0 0 0

E 7,200 0 0 0 0 0 0 0 0 0

F 7,200 0 0 0 0 0 0 0 0 0

G 7,200 0 0 0 0 0 0 0 0 0

H 7,200 0 0 0 0 0 0 0 0 0

I 7,200 0 0 4 0 0 0 0 0 0

J 7,200 0 271 1,149 0 8 1,271 4,449 0 0

K 7,200 0 0 1,810 0 0 17 4,268 0 0

L 7,200 0 774 1,995 0 154 841 3,392 0 0

Total 108,000 0 1,044 5,197 0 162 2,129 12,109 0 0

Total cost 

(million dollars per year)

2.870 3.604 5.311 * * * * 3.082 3.075
152 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

The results of the base case optimization run are 

shown in table 12 (optimization run 1). The 

optimization model yields individual rates for each 

injection and in-lieu cell for all fifty 6-month stress 

periods; however, it is the average results that are 

useful for practical implementation of a management 

strategy. An example sequence of the iterative solution 

is shown in table 13. In the final solution, the average 

annual cost is $2.87 million. The average annual in-lieu 

delivery is about 18,000 acre-ft and there is no 

additional injection. Although injection is more 

hydraulically efficient (that is, injecting water is 

directly at the control locations rather than reducing 

pumpage several miles inland), this is outweighed by 

the lower unit cost of in-lieu water. 

The optimization results can be analyzed to 

determine relative priorities for in-lieu delivery. One 

way to do this is by looking at the average reduced cost 

associated with the in-lieu delivery for each possible 

in-lieu well. Reduced cost can be defined as the change 

in the objective function resulting from a small change 

in the value of the variable (Schrage, 1997; Ahfeld and 

Mulligan, 2000). If computed in-lieu delivery at a 

given location and time period (Ilit) is at its upper 

bound (Il-maxi), then the reduced cost is negative. In 

this case, the reduced cost is the same as the dual price 

associated with the upper bound constraint on in-lieu 

delivery (equation 9) and represents the cost reduction 

that would result from increasing Il-maxi. If Ilit is 

greater than 0 but less than Il-maxi, then the reduced 

cost is 0. If Ilit equals 0, the reduced cost is positive. In 

this case, increasing Ilit from 0 has a detrimental effect 

on the objective function (equation 4). The average 

annual reduced cost for each in-lieu cell is shown in 

table 14. The more negative the average reduced cost, 

the greater the cost reduction resulting from increasing 

the upper bound on in-lieu delivery to that well. Based 

on these criteria, it can be seen from table 13 that the 

most benefit would be yielded by additional in-lieu 

delivery to wells 2, 9, 10, 14, 15, 18, and 19, all located 

close to the Dominguez Gap Barrier Project. 

The first sensitivity analysis tests the impact of 

changing the imposed average water-level constraint 

(changing Hmin-avg in equation 6) on the optimization 

results. The water-level constraint is first tightened to 

require minimum average heads to be greater than or 

equal to 5 ft above sea level. As shown in figure 47 and 

table 12 (optimization run 2), the average annual cost is 

$3.60 million, with average in-lieu delivery of about 

19,000 acre-ft/yr and average additional injection of 

about 1,000 acre-ft/yr. This additional injection occurs 

in cells J and L (table 12) the eastern part of the 

Dominguez Gap Barrier Project (fig. 46). The cost 

increase from the initial optimization for Hmin-avg

equal to 0 ft indicates that the annual cost of additional 

hydraulic protection from seawater intrusion is about 

$150,000 per foot. If equation 6 is tightened further to 

require average heads at control locations to be greater 

than or equal to 10 ft above sea level, then the average 

annual cost is $5.31 million, with average in-lieu 

delivery of about 16,000 acre-ft/yr and average 

additional injection of 5,200 acre-ft/yr (virtually all in 

the eastern part of the Dominguez Gap Barrier Project) 

(fig. 47; optimization run 3 in table 12). The additional 

annual cost of increasing the level of hydraulic 

protection from 5 ft to 10 ft is about $340,000 per foot. 

In other words, the additional costs of increasing 

hydraulic protection from 5 to 10 ft are greater than 

those for increasing from 0 to 5 ft. 

Table 13. Results from iterative solution for optimization run 1 (base case)

Iteration Cost 

(million dollars per year) Percentage change In lieu

(acre-feet per year)) Percentage change

1 2.843 17,770

2 2.904 2.14 18,160 2.19

3 2.882 −.73 18,020 −.77

4 2.870 −.45 17,930 −.50
Simulation-Optimization Analysis 153

Table 14. Average reduced cost for in lieu cells, for optimization run 1 

(base case)

In the second sensitivity analysis, the effects of 

the cost structure are evaluated. In the initial 

optimization, the ratio of unit costs of injection to in 

lieu is 3.30 ($528/acre-ft versus $168/acre-ft). The 

optimization model was run repeatedly, incrementally 

reducing that ratio (reducing the costs of injection 

relative to in-lieu delivery). As shown in figure 48 and 

table 12 (optimization runs 1, 4–7), small reductions in 

the ratio have little impact on the amounts of injection 

in comparison with in-lieu delivery. However, when 

that ratio becomes less than 2.0, the solution switches 

from in lieu to injection. Figure 48 is a tradeoff curve 

between relative costs and quantities of injection and 

in-lieu. At a cost ratio of 2.0 or greater, the lower unit 

costs of in-lieu delivery dominate the solution; at cost 

ratios of 1.5 or less, the hydraulic efficiency of 

injection becomes significant. When the costs of in lieu 

delivery and injection are equal (cost ratio of 1.0), the 

optimization results show average in-lieu delivery of 

about 2,200 acre-ft/yr and average additional injection 

(all in the eastern part of the Dominguez Gap Barrier) 

of about 12,100 acre-ft/yr (table 12). The base costs 

used in this analysis are provided by WRDSC. The 

tradeoff curve shown in figure 48 provides a means to 

evaluate the impacts of different unit costs on the 

optimization solutions.

For the third sensitivity analysis, the 

optimization was run using future scenario 2, rather 

than future scenario 1. The original cost structure was 

maintained and the minimum average head (Hmin-avg) 

was set to 0 in equation 6. As shown in table 12

(optimization run 8), total annual costs are 

$3.08 million per year (about $200,000, or 7 percent, 

greater than those of the base case optimization). Inlieu delivery is 19,300 acre-ft/yr (about 1,000 acre-ft 

more than in the base case optimization) with no 

additional injection. Although scenario 2 involves only 

changes (increases in pumpage) in the Central Basin, it 

has some effect on these optimization results for 

seawater-intrusion management in the West Coast 

Basin. The optimization also was rerun using scenario 

2 with a constant-flow boundary for Orange County. 

The optimization results were essentially unchanged 

(table 12, optimization run 9). This is consistent with 

the fact that the different boundary-condition 

assumptions for Orange County have little effect on 

future simulated water levels in the West Coast Basin 

(compare figs. 41 and 45). 

In lieu cells Average reduced cost 

(dollars per acre-foot per year)

1 50

2 −430

3 80

4 110

5 −50

6 −20

7 940

8 300

9 −320

10 −450

11 2,920

12 2,660

13 2,880

14 −970

15 −670

16 2,750

17 2,020

18 −790

19 −520
154 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

SUMMARY

Nearly one-hundred years after Mendenhall 

(1905a,b,c) first described the ground-water resources 

of the Los Angeles area, there is a continuing need to 

improve the scientific basis for regional ground-water 

management. To help address this need in the Central 

and West Coast Basins, the USGS has compiled 

existing data, collected extensive new data, conducted 

new characterizations of the regional geohydrology 

and geochemistry, and developed and applied groundwater flow simulation and optimization models. 

The data compilation centered on development 

of a GIS. The new data collected in this study focused 

RATIO OF INJECTION COST TO IN-LIEU COST on collecting hydraulic, geologic, and chemical data 

0

2

4

6

8

10

12

14

16

18

20

3.5 3 2.5 2 1.5 1

IN THOUSANDS OF ACRE-FEET PER YEAR

In-lieu

Injection

Base case cost ratio (3.3)

0

5

10

15

20

25

In lieu

Injection

Head

greater than

or equal to 0

Head

greater than

or equal to 5

Head

greater than

or equal to 10

Head

greater than

or equal to 0

Head

greater than

or equal to 5

Head

greater than

or equal to 10

CONSTRAINT ON AVERAGE HEADS AT COAST CONSTRAINT ON AVERAGE HEADS AT COAST

THOUSANDS OF ACRE-FEET PER YEAR

 COST, 

IN MILLIONS OF DOLLARS PER YEAR

0

1

2

4

5

6

3

Figure 47. Sensitivity of optimization results (injection rates, in lieu rates and total cost) to average head constraint, Los Angeles County, California.

Figure 48. Sensitivity of optimization reslts to relative cost of injection 

and in-lieu water, Los Angeles County, California.
Summary 155

from newly installed multiple-well monitoring sites. 

Chemical data also were collected from existing 

production and observation wells in the study area. All 

the new data collected as part of this study are included 

in a companion report by Land and others (2002). 

 The geohydrologic and geochemical 

characterizations of the study were based on the 

compiled and newly collected data. The geohydrologic 

analyses build on the important previous studies of 

Poland and his co-workers and the California 

Department of Water Resources. In this study, the 

complex three-dimensional aquifer system was divided 

into four aquifer systems—Recent, Lakewood, Upper 

San Pedro, and Lower San Pedro. A set of 

geohydrologic sections were developed and surfaces 

for the aquifer systems were generated by evaluating 

geophysical logs, drill cuttings, geochemistry, and 

other supplementary information. 

The geochemical analyses focused on 

developing a three-dimensional conceptualization of 

the regional geochemistry in order to better understand 

the ground-water flow system. Analyses of major ions, 

the stables isotopes of oxygen and hydrogen, and 

tritium and carbon-14 provided information on the 

sources of recharge and the movement and age of 

ground water in the study area. 

Dissolved-solids concentrations in many parts of 

the basin are low (less than 500 mg/L), and generally 

decrease with increasing depth and with increasing 

distance from the forebays. The chemical composition 

of most water grades from calcium-bicarbonate/sulfate 

to sodium-bicarbonate with increasing residence time 

in the aquifer system. Near the coast, several wells 

yielded sodium-chloride water high in dissolved solids.

Stable-isotope data reveal a distinct composition 

for natural recharge from the San Fernando Valley 

(about −47 per mil δD), San Gabriel Valley (about 

−55 δD per mil), and locally along the coastal plain and 

surrounding hills (greater than −43 per mil δD). Stableisotope data suggest that recharge to several wells 

located in and downgradient from the Montebello 

Forebay and near the seawater-barrier projects is 

attributable to a significant proportion of imported 

water. Generally, these wells also contain water with 

tritium greater than 8 TU, indicating that recharge 

occurred within the last 50 years. 

Water with less than measurable tritium is found 

in and downgradient from the Los Angeles Forebay 

and in most wells in the West Coast Basin, indicating 

an age for recharge exceeding 50 years. For these 

wells, uncorrected estimates of age from carbon-14 

measurements show that water in the West Coast Basin 

(56 pmc; 9,500 years before present) is much older 

than water in the Central Basin (28 pmc; 3,900 years 

before present). 

The ground-water simulation model was 

developed to integrate the information on the 

geohydrology and the ground-water flow system, 

quantify the three-dimensional ground-water budget, 

test alternative geohydrologic hypotheses about the 

basin, and assess the hydraulic effects of alternative 

ground-water-management scenarios. Development of 

the model required defining of boundary conditions, 

delineating aquifer elevations and hydraulic properties, 

compiling pumpage, spreading, and injection rates, and 

estimating areal recharge. The four-layer MODFLOW 

model was run for a steady-state simulation to 

approximate conditions in 1971 and for a transient 

simulation for the period 1971–2000. The model is 

generally effective in reproducing the spatial and 

temporal dynamics of the regional ground-water flow 

system over the simulation period. Specific areas 

where water levels or vertical gradients are not well 

reproduced by the model and important model 

assumptions and limitations were identified. Sensitivity 

of model results to hydraulic parameters and to the 

assumed conditions along the Orange County boundary 

were quantified.

The model was used to analyze the threedimensional ground-water budget. The model 

simulates large flows of water from the Montebello 

Forebay and relatively small flows across the NIU. The 

model simulates average 1971–2000 net inflow to the 

West Coast Basin of about 7,000 acre-ft/yr from the 

ocean (San Pedro and Santa Monica Bay). The model 

simulates average 1971-2000 net inflow to the Central 

Basin of about 6,000 acre-ft/yr through the Los 

Angeles Narrows, 24,000 acre-ft/yr through the 
156 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Whittier Narrows, and 8,000 acre-ft/yr from Orange 

County. The historical transient simulation indicates 

that there has been a net increase in ground-water 

storage throughout the study area from 1971-2000. 

There has been a net decrease in storage in the last five 

years of the simulation (1996–2000). 

Particle tracking was applied to simulate 

advective transport of water from the spreading 

grounds, from offshore, and from injection wells. The 

particle tracking from the spreading grounds yielded 

results that were consistent with tritium-based 

estimates of ground-water travel times from the 

Montebello Forebay if it was assumed that most 

transport within the Upper San Pedro aquifer system 

occurs within about 20 percent of the total aquifer 

thickness. This particle tracking indicates that most of 

the spread water reaches the Upper San Pedro aquifer 

system (model layer 3). The particle tracking of water 

from the coastline provides estimates of average 

advective velocities of landward flow. Particle tracking 

of injection water indicates that nearly all injected 

water has moved inland, providing recharge to the 

West Coast Basin. 

The simulation model also was used to evaluate 

two alternative future (2001–2025) ground-watermanagement scenarios for the Central and West Coast 

Basins. Scenario 1 assumes continued pumping at 

average current rates; scenario 2 assumes that pumpage 

at most wells in the Central Basin will increase by 

25 percent over the management period. For scenario 

1, water levels are generally constant or slightly 

increasing throughout the management period. For 

scenario 2, water levels decline by 25 to 50 ft in the 

Central Basin. If flows from Orange County are fixed 

in the model, simulated water-level declines in the 

Central Basin for scenario 2 are larger. 

A final application of the simulation model was 

to link it with an optimization algorithm to identify 

efficient strategies for hydraulic control of seawater 

intrusion. Future scenario 1 was assumed for 

background conditions for the base case. The 

optimization analysis considered the tradeoffs between 

increased injection and increased in-lieu delivery for 

maintaining hydraulic barriers to seawater intrusion. 

Given the current cost structure (the cost for injection 

water is more than three times that of in-lieu water), the 

optimization solution is to put all resources into 

purchase of additional in-lieu water. Preferential 

locations for in-lieu delivery near the Dominguez Gap 

Barrier Project were identified. 

Several sensitivity analyses were conducted with 

the optimization model. The sensitivity of the solution 

to the water-level constraints was tested by modifying 

the required lower bound on average water levels at 

control locations. As the required average water level 

was increased from 0 to 5 to 10 ft, the costs increased 

nonlinearly. The sensitivity of the solution to the cost 

structure also was tested by varying the relative costs 

of injection versus in-lieu water. When the cost of 

injection water relative to in-lieu water decreases 

below about 2, the solution shifts to injection water. 

Changing the assumed Orange County boundary 

condition did not affect the optimization results. 

Changing the assumed future conditions from scenario 

1 to scenario 2 resulted in a slight increase in in-lieu 

delivery.

REFERENCES CITED

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APPENDIXES
Appendix I 161

Appendix I. Geographic Information System

The GIS contains spatial data layers, databases, 

and other data files. Spatial data layers consist of 

COVERAGEs (points, lines, or polygons), GRIDs 

(raster data), and TINs (triangulated irregular network) 

created with ESRI's (Environmental Systems Research 

Institute) ArcGIS 8.1 and ArcView 3.2 software. 

Databases are maintained using Microsoft Access 

2000, along with other data files stored in Microsoft 

Excel, dbase and in INFO tables. The current platforms 

used include UNIX and NT servers, and Windows 

2000 workstations. Metadata for the spatial data layers 

are documented to Federal Geographic Data Center 

(FGDC) standards, easily searchable by extent, 

keyword, or other parameters.

The GIS structure consists of spatial data files 

related to tabular data files by common items. For 

example, a State well number from the wells coverage 

can be related to a set of water-quality records from the 

water- quality Access database. Databases are linked, 

sharing tables.

All the spatial data layers in the GIS are 

projected in the Universal Transverse Mercator (UTM) 

projection, zone 11, using the North American Datum 

of 1927 (NAD27). The UTM projection was chosen 

because a single UTM zone encompasses the entire 

study area, and because all distances, directions, 

shapes, and areas are reasonably accurate within that 

zone. The units of the projection are in meters. The 

coordinates of the spatial layers are stored as singleprecision values that allow as many as seven 

significant digits for each coordinate. Because of the 

distance from the equator north to the study area, the 

Y-direction coordinates are large (over 3 million). To 

maintain the positional integrity of the spatial layers, a 

value of 3.5 million meters was subtracted from all 

Y coordinates during the projection process.

Data files and spatial layers for this study were 

acquired and created in a variety of ways from public 

sources. Data files were created from ASCII files 

imported into an INFO database within ArcInfo or 

directly into Access. Several coverage-creation 

methods were used—including transforming page 

coordinates to projected coordinates from DXF files, 

importing ArcInfo coverages, and digitizing from 

paper or Mylar maps. In the case of wells or other point 

coverages, latitude and longitude were the primary 

location reference items. Where latitude and longitude 

were absent, the State well identification number was 

used as an estimate to plot wells within 1/8 mile using 

the Public Land Survey System (PLSS).

The spatial data layers in the GIS for this study 

include cultural, hydrologic, and geologic features. 

Cultural features include city centers, roads, and land 

use/land cover. Hydrologic features include wells, 

precipitation stations, and streams. Geologic features 

include faults, folds, and geology. 

An essential component of the GIS, for the 

geohydrologic and geochemical analysis described in 

this report, is well information. Specific well data 

include water levels, water quality, pumpage, and 

injection. Almost all well files were created from 

existing digital data, spreadsheets, or other applications 

from cooperators, and USGS measurements. In 

addition to well information, streamflow and 

precipitation data also were compiled.
162 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Appendix II. Well identification, Model Layer, and Aquifer-Systems information for U.S. Geological Survey Multiple-well Monitoring Sites, Los Angeles, 

California 

[Location of sites shown in figure 2A; state well Nos., see well-numbering diagram in text; Model Layer, see section on “Development of ground-water 

simulation model” in text and fig. 3; Aquifer Systems, see section on “Geochemical analysis in text and fig. 3; well depth and perforated interval, in feet below 

land surface; —, not included in model]

State

well No.

Local

designation Well depth Perforated interval Model 

layer

Aquifer 

systems

4S/13W-9H9 Carson-1 #1 1,010 990–1,010 3 Lower

4S/13W-9H10 Carson-1 #2 760 740–760 3 Lower

4S/13W-9H11 Carson-1 #3 480 460–480 3 Lower

4S/13W-9H12 Carson-1 #4 270 250–270 2 Lower

4S/11W-5P9 Cerritos-1 #1 1,215 1,155–1,175 4 Lower

4S/11W-5P10 Cerritos-1 #2 1,020 1,000–1,020 4 Lower

4S/11W-5P11 Cerritos-1 #3 630 610–630 3 Lower

4S/11W-5P12 Cerritos-1 #4 290 270–290 3 Lower

4S/11W-5P13 Cerritos-1 #5 200 180–200 2 Upper

4S/11W-5P14 Cerritos-1 #6 135 125–135 2 Upper

2S/12W-7J1 Commerce-1 #1 1,390 1,330–1,390 — Pico Unit

2S/12W-7J2 Commerce-1 #2 960 940–960 4 Lower

2S/12W-7J3 Commerce-1 #3 780 760–780 4 Lower

2S/12W-7J4 Commerce-1 #4 590 570–590 3 Lower

2S/12W-7J5 Commerce-1 #5 345 325–345 3 Lower

2S/12W-7J6 Commerce-1 #6 225 205–225 2 Upper

3S/12W-9J1 Downey-1 #1 1,190 1,170–1,190 3 Lower

3S/12W-9J2 Downey-1 #2 960 940– 960 3 Lower

3S/12W-9J3 Downey-1 #3 600 580–600 3 Lower

3S/12W-9J4 Downey-1 #4 390 370–390 2 Upper

3S/12W-9J5 Downey-1 #5 270 250–270 2 Upper

3S/12W-9J6 Downey-1 #6 110 90–110 1 Upper

3S/14W-13J5 Gardena-1 #1 990 970–990 4 Lower

3S/14W-13J6 Gardena-1 #2 465 445–465 3 Lower

3S/14W-13J7 Gardena-1 #3 365 345–365 3 Lower

3S/14W-13J8 Gardena-1 #4 140 120–140 2 Upper

3S/14W-17G3 Hawthorne-1 #1 990 910– 950 — Pico Unit

3S/14W-17G4 Hawthorne-1 #2 730 710–730 4 Lower

3S/14W-17G5 Hawthorne-1 #3 540 520–540 3 Lower

3S/14W-17G6 Hawthorne-1 #4 420 400–420 3 Lower
Appendix II 163

Appendix II. Well identification, Model Layer, and Aquifer-Systems information for U.S. Geological Survey Multiple-well Monitoring Sites, Los Angeles, 

California—Continued

3S/14W-17G7 Hawthorne-1 #5 260 240–260 2 Upper

3S/14W-17G8 Hawthorne-1 #6 130 110–130 2 Upper

2S/13W-22C1 Huntington Park-1 #1 910 890–910 3 Lower

2S/13W-22C2 Huntington Park-1 #2 710 690–710 3 Lower

2S/13W-22C3 Huntington Park-1 #3 440 420–440 3 Lower

2S/13W-22C4 Huntington Park-1 #4 295 275–295 2 Upper

2S/13W-22C5 Huntington Park-1 #5 134 114–134 1 Upper

2S/14W-28M3 Inglewood-1 #1 1,400 1,380–1,400 — Pico Unit

2S/14W-28M4 Inglewood-1 #2 885 865–885 — Pico Unit

2S/14W-28M5 Inglewood-1 #3 450 430–450 3 Lower

2S/14W-28M6 Inglewood-1 #4 300 280–300 3 Lower

2S/14W-28M7 Inglewood-1 #5 170 150–170 2 Upper

2S/14W-26N3 Inglewood-2 #1 860 800–840 — Pico Unit

2S/14W-26N4 Inglewood-2 #2 470 450–470 — Pico Unit

2S/14W-26N5 Inglewood-2 #3 350 330–350 3 Lower

2S/14W-26N6 Inglewood-2 #4 245 225–245 3 Lower

3S/11W-26E2 La Mirada-1 #1 1,150 1,130–1,150 4 Lower

3S/11W-26E3 La Mirada-1 #2 985 965–985 4 Lower

3S/11W-26E4 La Mirada-1 #3 710 690–710 3 Lower

3S/11W-26E5 La Mirada-1 #4 490 470–490 3 Lower

3S/11W-26E6 La Mirada-1 #5 245 225–245 2 Upper

4S/12W-05H5 Lakewood-1 #1 1,009 989–1,009 4 Lower

4S/12W-5H6 Lakewood-1 #2 660 640– 660 3 Lower

4S/12W-5H7 Lakewood-1 #3 470 450–470 3 Lower

4S/12W-5H8 Lakewood-1 #4 300 280–300 2 Upper

4S/12W-5H9 Lakewood-1 #5 160 140–160 2 Upper

4S/12W-5H1 Lakewood-1 #6 90 70–90 1 Upper

4S/14W-26A2 Lomita-1 #1 1,340 1,240–1,260 4 Lower

4S/14W-26A3 Lomita-1 #2 720 700–720 3 Lower

4S/14W-26A4 Lomita-1 #3 570 550–570 3 Lower

4S/14W-26A5 Lomita-1 #4 420 400–420 3 Lower

State

well No.

Local

designation Well depth Perforated interval Model 

layer

Aquifer 

systems
164 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Appendix II. Well identification, Model Layer, and Aquifer-Systems information for U.S. Geological Survey Multiple-well Monitoring Sites, Los Angeles, 

California—Continued

4S/14W-26A6 Lomita-1 #5 240 220–240 2 Upper

4S/14W-26A7 Lomita-1 #6 120 100–120 2 Upper

4S/12W-25G1 Long Beach-1 #1 1,470 1,430–1,450 4 Lower

4S/12W-25G2 Long Beach-1 #2 1,250 1,230–1,250 4 Lower

4S/12W-25G3 Long Beach-1 #3 990 970–990 3 Lower

4S/12W-25G4 Long Beach-1 #4 619 599–619 3 Lower

4S/12W-25G5 Long Beach-1 #5 420 400–420 3 Lower

4S/12W-25G6 Long Beach-1 #6 175 155–175 2 Upper

4S/13W-1N3 Long Beach-2 #1 1,090 970–990 — Pico Unit

4S/13W-1N4 Long Beach-2 #2 740 720–740 4 Lower

4S/13W-1N5 Long Beach-2 #3 470 450–470 3 Lower

4S/13W-1N6 Long Beach-2 #4 300 280–300 3 Lower

4S/13W-1N7 Long Beach-2 #5 180 160–180 2 Upper

4S/13W-1N8 Long Beach-2 #6 115 95–115 2 Upper

2S/13W-17F1 Los Angeles-1 #1 1,370 1,350–1,370 4 Lower

2S/13W-17F2 Los Angeles-1 #2 1,100 1,080–1,100 3 Lower

2S/13W-17F3 Los Angeles-1 #3 940 920–940 3 Lower

2S/13W-17F4 Los Angeles-1 #4 660 640–660 3 Lower

2S/13W-17F5 Los Angeles-1 #5 370 350–370 3 Lower

2S/11W-18C4 Pico Rivera-1 #1 900 860–900 — Pico Unit

2S/11W-18C5 Pico Rivera-1 #2 480 460–480 4 Lower

2S/11W-18C6 Pico Rivera-1 #3 400 380–400 3 Lower

2S/11W-18C7 Pico Rivera-1 #4 190 170–190 3 Lower

2S/12W-25G3 Pico Rivera-2 #1 1,200 1,180–1,200 4 Lower

2S/12W-25G4 Pico Rivera-2 #2 850 830–850 3 Lower

2S/12W-25G5 Pico Rivera-2 #3 580 560–580 3 Lower

2S/12W-25G6 Pico Rivera-2 #4 340 320–340 3 Lower

2S/12W-25G7 Pico Rivera-2 #5 255 235–255 2 Upper

2S/12W-25G8 Pico Rivera-2 #6 120 100-120 1 Upper

2S/12W-26D9 Rio Hondo-1 #1 1,150 1,110-1,130 4 Lower

2S/12W-26D10 Rio Hondo-1 #2 930 910–930 3 Lower

State

well No.

Local

designation Well depth Perforated interval Model 

layer

Aquifer 

systems
Appendix II 165

Appendix II. Well identification, Model Layer, and Aquifer-Systems information for U.S. Geological Survey Multiple-well Monitoring Sites, Los Angeles, 

California—Continued

2S/12W-26D11 Rio Hondo-1 #3 730 710–730 3 Lower

2S/12W-26D12 Rio Hondo-1 #4 450 430–450 3 Lower

2S/12W-26D13 Rio Hondo-1 #5 300 280–300 2 Upper

2S/12W-26D14 Rio Hondo-1 #6 160 140–160 1 Upper

3S/11W-9D1 Santa Fe Springs-1 #1 1,410 1,290–1,310 — Pico Unit

3S/11W-9D2 Santa Fe Springs-1 #2 845 825–845 4 Lower

3S/11W-9D3 Santa Fe Springs-1 #3 560 540–560 3 Lower

3S/11W-9D4 Santa Fe Springs-1 #4 285 265–285 3 Lower

3S/12W-6B4 South Gate-1 #1 1,460 1,440–1,460 4 Lower

3S/12W-6B5 South Gate-1 #2 1,340 1,320–1,340 3 Lower

3S/12W-6B6 South Gate-1 #3 930 910–930 3 Lower

3S/12W-6B7 South Gate-1 #4 585 565–585 3 Lower

3S/12W-6B8 South Gate-1 #5 250 220–240 2 Upper

3S/11W-2K4 Whittier-1 #1 1,280 1,180–1,200 3 Lower

3S/11W-2K5 Whittier-1 #2 940 920–940 3 Lower

3S/11W-2K8 Whittier-1 #3 620 600–620 3 Lower

3S/11W-2K6 Whittier-1 #4 470 450–470 3 Lower

3S/11W-2K7 Whittier-1 #5 220 200–220 2 Upper

3S/13W-8J1 Willowbrook-1 #1 905 885–905 4 Lower

3S/13W-8J2 Willowbrook-1 #2 520 500–520 3 Lower

3S/13W-8J3 Willowbrook-1 #3 380 360–380 3 Lower

3S/13W-8J4 Willowbrook-1 #4 220 200–220 2 Upper

4S/13W-28A3 Wilmington-1 #1 1,035 915–935 4 Lower

4S/13W-28A4 Wilmington-1 #2 800 780–800 4 Lower

4S/13W-28A5 Wilmington-1 #3 570 550–570 3 Lower

4S/13W-28A6 Wilmington-1 #4 245 225–245 3 Lower

4S/13W-28A7 Wilmington-1 #5 140 120–140 2 Upper

4S/13W-32F1 Wilmington-2 #1 1,030 950–970 4 Lower

4S/13W-32F2 Wilmington-2 #2 775 755–775 3 Lower

4S/13W-32F3 Wilmington-2 #3 560 540–560 3 Lower

4S/13W-32F4 Wilmington-2 #4 410 390–410 3 Lower

4S/13W-32F5 Wilmington-2 #5 140 120–140 2 Upper

State

well No.

Local

designation Well depth Perforated interval Model 

layer

Aquifer 

systems
166 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Appendix III. Correlation between Specific Conductance and Dissolved-Solids Concentration

DSC = 0.59 (Specific Conductance) + 2

R2

 = 0.99

100

1,000

10,000

100,000

100 1,000 10,000 100,000

SPECIFIC CONDUCTANCE (SC), IN MICROSIEMENS PER

CENTIMETER AT 25 DEGREES CELSIUS 

DISSOLVED-SOLIDS CONCENTRATION (SUM), IN MILLIGRAMS PER LITER 

C

Dissolved-solids concentrations (DSC), commonly referred to as total dissolved solids (TDS), is a

measure of the total amount of dissolved ions in a water, and give an indication as to the overall

quality of water. TDS concentrations are commonly determined by weighing the residue of a known 

volume of water following evaporation at 180 degrees Celsius.

Dissolved-solids concentrations discussed in this report are calculated values, computed by summing 

all major (Ca, Mg, Na, Cl, SO4, alk, Si) and minor (K, Fe, Mn, Sr, B, F, NO3) constituents. For a few 

samples (for which a complete chemical analysis was not available), dissolved solids concentrations

were estimated from measurements of specific conductance taken in the field.

The relation between TDS and specific conductance (SC) is nearly linear, but the slope of this line

varies according to the chemical composition of a particular water (Hem, 1992). The regression of

dissolved-solids and specific-conductance measurements taken as part of this study yield a slope 

of 0.59 with a correlation coefficient of 0.99 (r2 = 0.99). This is similar to the slope computed during 

earlier work in the basin (Piper and Garrett, 1953).
APPENDIX IV 167

Appendix IV. Parameters used to generate model layer elevation surfaces[NA, not applicable; nugget effect and sill are expressed in terms of variance of elevation (feet squared); correlation length is expressed in terms of X–Y space measured in UTM coordinates (meters); 

anisotropy, expressed as a ratio of variability between two axes; the angle is measured from the positive x-axis to the first axis; nested spherical model requires specification two values for both sill and 

correlation length; the gridding program, Surfer 7 (Golden Software, 1999) was used to generate the surfaces]

11.238 ratio at 178.2 degrees

Layer Aquifer system Function type used Description of model used Nugget effect (in feet squared) Sill (in feet squared) Correlation length (meters) Slope Anisotropy

1 Recent Radial basis 

function interpolation

Multiquadratic 

kernal

NA NA NA NA No

2 Lakewood Block kriging Nested spherical 

models with nugget

2,000 8,000 10,000 NA No

7,000 24,000

3 Upper San 

Pedro

Block kriging Gaussian model 

with nugget

16,200 66,200 5,000 NA Yes1

4 Lower San 

Pedro

Block kriging Linear model 

with nugget

37,400 NA NA 8.03 No
168 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Appendix V: Estimation of mountain front recharge for 1970–71

The areas contributing to mountain-front 

recharge range in elevation from sea level to 2,100 ft 

with a mean of about 560 ft. The active onshore model 

area averages about 170 feet in comparison. The 

specific geographic areas are the Santa Monica 

Mountains and Elysian Hills to the north, the Repetto 

Hills, Merced Hills and Puente Hills to the northeast, 

and the Palos Verdes Hills to the southwest (fig. 1 in 

Appendix V).

Contributing watersheds were delineated for the 

entire basin using a 30-meter USGS digital elevation 

model (DEM) and various ArcInfo hydrologic 

functions. Delineation steps included clipping the 

DEM to the study area; filling in the DEM sinks 

(imperfections in the DEM); creating a flow direction 

model to determine the steepest down-slope direction 

of flow; creating a flow accumulation model to find 

areas where water congregates, such as in a stream 

course; and creating a stream network to simulate 

possible stream locations. These steps are standard 

hydrologic functions performed in ArcInfo for 

delineating a watershed (Maidment and Djokic, 2000).

Once the individual watersheds were delineated 

for the entire study area, the domain of the groundwater model was overlaid to clip out the areas that 

extend beyond the model. Areas already accounted for 

with head-dependent boundary conditions at the Los 

Angeles Narrows, the Whittier Narrows, and the 

Orange County boundary were excluded. The 

watersheds were labeled according to the zone of the 

ground-water model into which the water flowed (fig. 1 

in Appendix V). The areas of these contributing 

watersheds are given in table 1 in Appendix V. 

A precipitation grid was then constructed using a 

precipitation station database compiled by the Los 

Angeles County Department of Public Works. Wateryear totals were computed and the stations georeferenced. Only precipitation stations that were 

located in the basin model area and the surrounding 

mountains were used. 

Three surface-extrapolation methods were 

considered for producing the precipitation-grid surface 

in ArcInfo: inverse distance weighting (IDW), kriging, 

and a simple regression model. IDW and kriging both 

weight the data on the basis of their spatial relation to 

one another. Therefore, with the sparse precipitation 

data in the mountains, a biased grid reflecting the 

precipitation amounts of the basin floor would be 

created. To illustrate this point, precipitation values in 

the Puente Hills were more closely related to values in 

the Santa Monica Mountains 30 mi away than they 

were to precipitation values on the basin floor 3 mi 

away. More advanced kriging algorithms, such as cokriging, may be able to compensate for this and could 

be considered in the future. 

The simple method chosen for this application 

was regression. The regression method is based on the 

assumption that as altitude increases, precipitation 

increases (Hevesi and others, 1991). An equation can 

be derived that correlates precipitation with elevation. 

Different equations were tested in fitting the data, 

including exponential and logarithmic functions. A 

simple linear regression produced the highest 

R-squared value and therefore was used (fig. 2 in 

Appendix V). 

By using a clipped USGS 30-meter DEM and 

applying the regression on a cell-by-cell basis, a 

precipitation grid was interpolated using a cell size of 

100 m (328 ft). The results for water year 1971 are 

included in table 1 in Appendix V. 

Mountain-front recharge for 1970–71 was 

estimated from this precipitation grid by applying 

simple percentages of precipitation. In a report on 

ground water in the Great Basin area of Nevada, 

Maxey and Eakin (1949) estimated the following 

percentages to apply for recharge estimation: 0 percent 

for less than 8 in., 3 percent for 8 to 10 in., 7 percent for 

10 to 12 in., 15 percent for 12 to 15 in., and 25 percent 

for greater than 15 in. By applying the percentages to 

each cell in the precipitation grid, a recharge grid was 

produced. Average recharge per watershed can be 

calculated by using ArcInfo zonal functions. Results 

are given in table 1 in Appendix V. 

The resulting estimated values of mountain-front 

recharge shown in the last column of the table were 

applied to represent steady state (1970–71) mountainfront recharge in the model. These values are 

considered to be reasonable estimates, but there are 

many limitations to this simple approach that was 

developed for recharge in the Great Basin (Miller, 

1977), especially when applied to a different 

physiographic area. D’Agnese and others (1997) 

summarized some important limitations of the MaxeyEakin method, including the fact that the method does 

not considering important factors such as slope aspect, 

interbasin flow, permeabilities of different deposits, 

soil moisture, and vegetation differences.
Appendix V 169

See Appendix V Table 1

EXPLANATION

Downey

Station 107D

601

601

401 203 205

301

303

1001

1002

302

204

202

201

402

Precipitation station

Model subareas

Contributing watershed

Model onshore area

0 10 MILES

0 10 KILOMETERS

33°

40'

50'

34°

00'

118°30' 11 20' 10' 8°00'

Repetto Hills

Elysia

H n ills

Merced Hills

Palos Verdes Hills

Puente Hills

Santa Monica Mountains

Hollywood Hills

Appendix V Figure 1.Location of precipitation stations and contributing watersheds used for estimating recharge, Los Angeles County, California.
170 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Appendix V, Table 1. Estimated mountain front recharge for water year 1971

Model zone Contributing watershed Area of watersheds

(meters squared)

Average precipitation ,

in inches

Recharge.

in acre feet

Los Angeles Forebay 201 10,280,000 13.6 440

202 9,380,000 13.9 440

203 3,160,000 14.6 170

204 15,550,000 14.6 840

205 18,560,000 14.8 1,050

Montebello Forebay 301 11,660,000 14.2 540

302 2,990,000 13.9 130

303 8,310,000 13.9 430

Hollywood Basin 401 46,870,000 17.4 4,050

402 4,870,000 14.4 250

West Coast Basin 501 15,920,000 16.2 1170

502 15,250,000 15.5 1000

Santa Monica Basin 601 86,800,000 19.3 8,540

Whittier Area 1001 25,960,000 16.5 2,080

1002 25,620,000 14.4 1,350

TOTAL 308,660,000 22,470
Appendix V 171

Precipitation = 0.0236 elevation + 10.877

 Correlation coefficient = 0.5005

0

5

10

15

20

25

30

0 50 100 150 200 250 300 350 400 450

ELEVATION, IN METERS

PRECIPITATION, IN INCHES

Appendix V Figure 2.Correlation between precipitation and elevation, 1970–71, Los Angeles County, California.
172 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

Appendix VI. Hydrographs of simulated and measured water levels, 1971–2000

1970 2002 1980 1990

100

0

-25

-50

75

25

50

3S/12W-9J1-3 Downey-1 #1, 2, 3

1170-1190, 940-960, 580-600 (29, 50)

Central Basin Pressure layer 3 USGS

YEAR

WATER LEVEL,

IN FEET ABOVE SEA LEVEL

EXPLANATION FOR APPENDIX VI HYDROGRAPHS

Model layer

Subarea USGS site

Local designation

Simulated water level

Measured

water levels

Model row and column

Locations of wells are shown on figure 23

State well number

Perforated interval,

in feet below land surface
Appendix VI 173

1970 2002 1980 1970 2002 1990 1980 1990

1970 2002 1980 1970 2002 1990 1980 1990

50 0

125

100

75

200

150

175

50

125

100

75

200

150

175

Montebello Forebay layer 2 USGS 

Montebello Forebay layer 1 USGS Montebello Forebay layer 2 USGS 

Montebello Forebay layer 1 USGS 

Montebello Forebay layer 1

Montebello Forebay layer 1 

Montebello Forebay layer 2 USGS 

Montebello Forebay layer 2

Montebello Forebay layer 3 USGS 

Montebello Forebay layer 3 USGS 

150

50

25

0

125

75

100

75

50

25

150

100

125

0

75

50

25

150

100

125

75

50

25

150

100

125

0

125

150

25

0

100

50

75

200

100

75

50

175

125

150

100

0

-25

-50

75

25

50

200

100

75

50

175

125

150

2S/12W-25G8 Pico Rivera-2 #6

100-120 (29, 50)

2S/12W-26D14 Rio Hondo-1 #6

140-160 (35, 65)

2S/12W-14J1 1590F 

35-71 (19, 54)

2S/12W-33L3 1554F 

80-119 (25, 49)

2S/11W-18C7 Pico Rivera-1 #4 

170-190 (18, 57)

2S/12W-25G4-6 Pico Rivera-2 #2, 3, 4 

830-850, 560-580, 320-340 (29, 50)

2S/11W-18C6 Pico Rivera-1 #3

380-400 (18, 57)

2S/12W-24MO3 1601P/T

154-174 (21, 55)

2S/12W-26D13 Rio Hondo-1 #5

280-300 (22, 52)

2S/12W-25G7 Pico Rivera-2 #5

235-255 (29, 50)

YEAR YEAR

YEAR YEAR

WATER LEVEL, IN FEET ABOVE SEA LEVEL
174 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

1970 2002 1980 1990 1970 2002 1980 1990

1970 2002 1980 1970 2002 1990 1980 1990

150

50

25

0

0

125

75

100

50

125

100

75

200

150

175

150

50

25

0

125

75

100

75

50

25

150

100

125

50

-50

-75

-100

25

-25

0

0

25

-25

-50

100

50

75

0

25

-25

-50

100

50

75

50

-50

-75

-100

25

-25

0

75

-25

-50

-75

50

0

25

50

-50

-75

-100

25

-25

0

WATER LEVEL, IN FEET ABOVE SEA LEVEL

Montebello Forebay layer 3 USGS 

Los Angeles Forebay layer 3 USGS 

Los Angeles Forebay layer 3

Montebello Forebay layer 4 USGS 

Montebello Forebay layer 4 USGS 

Montebello Forebay layer 4 USGS 

Los Angeles Forebay layer 2 USGS 

Los Angeles Forebay layer 2 USGS 

Los Angeles Forebay layer 3 USGS 

Los Angeles Forebay layer 3 USGS 

2S/12W-26D10-12 Rio Hondo-1 #2, 3, 4

910-930, 710-730, 430-450 (22, 52)

2S/13W-22C4 Huntington Park-1 #4

275-295 (20, 39)

2S/13W-22C1-3 Huntington Park-1 #1, 2, 3

890-910, 690-710, 420-440 (20, 39)

2S/13W-10A1 2778

160-645 (16, 40)

2S/11W-18C5 Pico Rivera-1 #2

460-480 (18, 57)

2S/12W-25G3 Pico Rivera-2 #1

1180-1200 (29, 50)

2S/12W-26D9 Rio Hondo-1 #1

1110-1300 (22, 52)

2S/12W-7J6 Commerce-1 #6

205-225 (29, 50)

2S/12W-7J4,5 Commerce-1 #4, 5

570-590, 325-345 (29, 50)

2S/13W-17F2-5 Los Angeles-1 #2, 3, 4, 5

1,080-1,100, 920-940, 640-660, 350-370 (19, 35)

YEAR YEAR

YEAR YEAR
Appendix VI 175

1970 2002 1980 1970 2002 1990 1980 1990

1970 2002 1980 1970 2002 1990 1980 1990

100

0

-25

-50

75

25

50

30

-70

-95

-120

5

-45

-20

75

-25

-50

-75

50

0

25

175

75

50

25

150

100

125

200

100

75

50

175

125

150

200

100

75

50

175

125

150

75

50

25

150

100

125

0

75

50

25

150

100

125

0

100

0

-25

-50

75

25

50

Whittier Area layer 2

Whittier Area layer 2 USGS

Whittier Area layer 3 USGS

Los Angeles Forebay layer 4 USGS 

Los Angeles Forebay layer 4 USGS 

2S/13W-17F1 Los Angeles-1 #2

1350-1370 (19, 35)

2S/11W-33E2 1654H

(25, 61)

3S/11W-2K7 Whittier-1 #5

200-220 (27, 66) 

3S/11W-2K4,5,8,6 Whittier-1 #1, 2, 3, 4

1180-1200, 920-940, 600-620, 450-470 (27, 66)

Whittier Area layer 3 USGS

Whittier Area layer 4 USGS

Central Basin Pressure layer 1 USGS

Central Basin Pressure layer 1 USGS

3S/11W-9D3, 4 Santa Fe Springs-1 #3, 4

540-560, 265-285 (28, 60)

3S/11W-9D2 Santa Fe Springs-1 #2

825-845 (28, 60)

3S/12W-9J6 Downey-1 #6

90-110 (29, 50)

4S/12W-5H10 Lakewood-1 #6

70-90 (38, 48)

2S/12W-7J2-3 Commerce-1 #2, 3

940-960, 760-780 (29, 50)

125

25

0

-25

100

50

75

Central Basin Pressure layer 1

3S/12W-1A6 1615P

91-192 (26, 56)

YEAR YEAR

YEAR YEAR

WATER LEVEL, IN FEET ABOVE SEA LEVEL
176 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

1970 2002 1980 1970 2002 1990 1980 1990

1970 2002 1980 1970 2002 1990 1980 1990

30

-70

-95

-120

5

-45

-20

-50

-75

-100

-125

25

-25

0

100

0

-25

-50

75

25

50

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

100

0

-25

-50

75

25

50

100

0

-25

-50

75

25

50

-50

-75

-100

-125

25

-25

0

Central Basin Pressure layer 2

3S/12W-8L3 1537A

126-176, 221-236 (30, 49)

3S/12W-26E6 La Mirada-1 #5

225-245 (35, 65)

3S/12W-6B8 South Gate-1 #5

220-240 (26, 45)

3S/12W-9J4, 5 Downey-1 #4, 5

370-390, 250-270 (29, 50)

3S/13W-8J4 Willowbrook-1 #4

200-220 (29, 36)

4S/11W-5P13,14 Cerritos-1 #5, 6

180-200, 125-135 (39, 59)

4S/12W-5H8, 9 Lakewood-1 #4, 5

280-300, 140-160 (38, 48)

4S/12W-25G5-14 Long Beach-1 #6

155-175 (46, 55)

4S/13W-1N7,8 Long Beach-2 #5, 6

160-180, 95-115 (39, 42)

Central Basin Pressure layer 2 USGS

Central Basin Pressure layer 2 USGS

Central Basin Pressure layer 2 USGS

Central Basin Pressure layer 2 USGS

Central Basin Pressure layer 2 USGS

Central Basin Pressure layer 2 USGS

Central Basin Pressure layer 2 USGS

Central Basin Pressure layer 2 USGS

25

-75

-100

-150

0

-50

-25

2S/14W-26N5,6 Inglewood-2 #3, 4

330-350, 225- 245 (23, 29)

Central Basin Pressure layer 3 USGS

YEAR YEAR

YEAR YEAR

WATER LEVEL, IN FEET ABOVE SEA LEVEL
Appendix VI 177

1970 2002 1980 1970 2002 1990 1980 1990

1970 2002 1980 1970 2002 1990 1980 1990

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

100

0

-25

-50

75

25

50

50

-50

-75

-100

25

-25

0

75

-25

-50

-75

50

0

25

20

-70

-95

-120

5

-45

-20

-50

-75

-100

-125

25

-25

0

3S/11W-26E4, 5 La Mirada-1 #3, 4

690-710, 470- 490 (35, 65) 

3S/12W-6B5-7 South Gate-1 #2, 3, 4

1,320-1,340, 910-930, 565-585 (26, 45)

3S/12W-9J1-3 Downey-1 #1, 2, 3

1,170-1,190, 940-960, 580-600 (29, 50)

3S/13W-8J2, 3 Willowbrook-1 #2, 3

500-520, 360-380 (29, 36)

4S/11W-5P11,12 Cerritos-1 #3, 4

610-630, 270-290 (39, 59)

4S/12W-5H6, 7 Lakewood-1 #2, 3

640-660, 450-470 (38, 48)

4S/12W-25G3-5 Long Beach-1 #3, 4, 5

970-990, 599-619, 400-420 (46, 55)

Central Basin Pressure layer 3 USGS

Central Basin Pressure layer 3 USGS

Central Basin Pressure layer 3 USGS

Central Basin Pressure layer 3 USGS

Central Basin Pressure layer 3 USGS

Central Basin Pressure layer 3 USGS

Central Basin Pressure layer 3 USGS

-50

-75

-100

-125

-25

25

0 Central Basin Pressure layer 3 USGS

4S/13W-01N5,6 Long Beach-2 #3, 4

450-470, 280-300 (39, 42)

50

-50

-75

-100

25

-25

0

Central Basin Pressure layer 3

2S/13W-32C4 1434J

604-785 (24, 35)

50

-50

-75

-100

25

-25

0

2S/14W-22P4 1362P

285-322 (21, 27)

Central Basin Pressure layer 3

YEAR YEAR

YEAR YEAR

WATER LEVEL, IN FEET ABOVE SEA LEVEL
178 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

1970 2002 1980 1970 2002 1990 1980 1990

1970 2002 1980 1970 2002 1990 1980 1990

0

-100

-125

-150

-25

-75

-50

50

-50

-75

-100

25

-25

0

-50

-75

-100

-125

25

-25

0

25

-75

-100

-125

0

-50

-25

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

WATER LEVEL, IN FEET ABOVE SEA LEVEL

3S/12W-31E3 913E

701-933 (36, 45)

3S/13W-21R1 851F

366-525 (33, 38)

4S/12W-10G1 975A

367-388 (40, 52)

4S/13W-12K1 906D

915-1,000 (41, 43)

3S/11W-26E2,3 La Mirada-1 #1, 2

1,130-1,150, 965-985 (35, 65)

3S/12W-6B4 South Gate-1 #1

1,440-1,460 (26, 45)

Central Basin Pressure layer 3

Central Basin Pressure layer 3

Central Basin Pressure layer 3

Central Basin Pressure layer 3

Central Basin Pressure layer 4 USGS

Central Basin Pressure layer 4 USGS

-50

-75

-100

25

-25

0

-125

Central Basin Pressure layer 3

4S/12W-28H9 460K

143-550 (48, 50)

50

-50

-75

-100

25

-25

0

Central Basin Pressure layer 3

3S/12W-26C2 981C

568-590 ( 34, 53)

50

-50

-75

-100

25

-25

0

Central Basin Pressure layer 4 USGS

3S/13W-8J1 Willowbrook-1 #1

885-905 (29, 36)

75

-25

-50

-75

50

0

25

Central Basin Pressure layer 4 USGS

4S/11W-5P9-10 Cerritos-1 #1, 2 

1,155-1,175, 1,000-1,020 (39, 59)

YEAR YEAR

YEAR YEAR
Appendix VI 179

1970 2002 1980 1970 2002 1990 1980 1990

1970 2002 1980 1970 2002 1990 1980 1990

-50

-75

-100

-125

25

-25

0

30

-70

-95

-120

5

-45

-20

-50

-75

-100

-125

25

-25

0

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

25

-75

-100

-150

0

-50

-25

50

-50

-75

-100

25

-25

0

4S/12W-5H5 Lakewood-1 #1

989-1,019 (38, 48)

4S/12W-25G1,2 Long Beach-1 #1, 2

1,430-1,450, 1,230-1,250 (46, 55)

4S/13W 1N4 Long Beach-2 #2

720-740 (39, 42) 

2S/13W-36F2 1504C

978-1,276 (24, 43)

4S/12W-25E1 500D

1,124-1,146 (46, 54)

4S/12W-32G1 441

120-130 (48, 48)

2S/14W-28M7 Inglewood-1 #5

150-170 (23, 25)

3S/14W-13J8 Gardena-1 #4

120-140 (31, 32)

Central Basin Pressure layer 4 USGS

Central Basin Pressure layer 4 USGS

Central Basin Pressure layer 4 USGS

Central Basin Pressure layer 4

Central Basin Pressure layer 4

West Coast Basin layer 2

West Coast Basin layer 2 USGS

West Coast Basin layer 2 USGS

50

-50

-75

-100

25

-25

0 2S/14W-14F2 1380

(19, 29)

Central Basin Pressure layer 4 

YEAR YEAR

YEAR YEAR

WATER LEVEL, IN FEET ABOVE SEA LEVEL

50

-50

-75

-100

25

-25

0

3S/14W-17G7, 8 Hawthorne-1 #5, 6

240-260, 110-130 (30, 24)

West Coast Basin layer 2 USGS
180 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

1970 2002 1980 1970 2002 1990 1980 1990

1970 2002 1980 1990 1970 2002 1980 1990

-50

-75

-100

-125

25

-25

0

-50

-75

-100

-125

25

-25

0

50

-50

-75

-100

25

-25

0

125

25

0

-25

100

50

75

-50

-75

-100

-125

25

-25

0

25

-75

-100

-150

0

-50

-25

4S/13W-32F5 Wilmington-2 #5

120-140 (48, 35)

4S/13W-9H12 Carson-1 #4 

250-270 (40, 38)

4S/13W-28A7 Wilmington-1 #5

120-140 (46, 37) 

3S/15W-13H9 1308T

190-225 (30, 20)

4S/13W-30G1 310C

210-420 (46, 33)

2S/14W-28M5, 6 Inglewood-1 #3, 4

430-450, 280-300 (23, 25)

West Coast Basin layer 2

4S/14W-26A6,7 

240-120 (45, 29)

Lomita layer 2

West Coast Basin layer 2 USGS

West Coast Basin layer 2 USGS

West Coast Basin layer 2 USGS

West Coast Basin layer 3 USGS

West Coast Basin layer 3 

50

-50

-75

-100

25

-25

0

3S/14W-13J6, 7 Gardena-1 #2, 3

445-465, 345-365 (31, 32)

West Coast Basin layer 3 USGS

YEAR YEAR

YEAR YEAR

WATER LEVEL, IN FEET ABOVE SEA LEVEL

50

-50

-75

-100

25

-25

0

4S/14W-2N4 PM-3 Madrid #4

240-280, 123-145 (40, 28)

West Coast Basin layer 2

50

-50

-75

-100

25

-25

0

4S/14W-4K PM-4 Mariner #4

200-240 (39, 24)

West Coast Basin layer 2
Appendix VI 181

1970 2002 1980 1970 2002 1990 1980 1990

1970 2002 1980 1990 1970 2002 1980 1990

-50

-75

-100

-125

25

-25

0

-50

-75

-100

-125

25

-25

0

50

-50

-75

25

-25

0

50

-50

-75

-100

25

-25

0

50

-50

-75

-100 -100

25

-25

0

50

-50

-25

-75

25

-25

0

0

-100

-125

-150

-25

-75

-50

0

-100

-125

-150

-25

-75

-50 4S/13W-28A5, 6 Wilmington-1 #3, 4

550-570, 225-245 (46, 37)

4S/13W-32F2-4 Wilmington-2 #2, 3, 4

755-775, 540-560, 390-410 (48, 35)

4S/13W-9H9-11 Carson-1 #1, 2, 3

990-1,010, 740-760, 460-480 (40, 38) 

4S/14W-26A2-4 Lomita-1 #2, 3, 4

700-720, 550-570, 400-420 (45, 29)

3S/14W-22L1 760C 

352-458 ( 33, 27)

4S/13W-21H5 868H

440-709 (44, 38)

4S/13W-23B2 888F

650-900 (43, 41)

4S/14W-01F2 794B

477-540 (38, 31)

West Coast Basin layer 3

West Coast Basin layer 3

West Coast Basin layer 3

West Coast Basin layer 3 USGS

West Coast Basin layer 3 USGS

West Coast Basin layer 3 USGS

West Coast Basin layer 3 USGS

West Coast Basin layer 3 

0

-100

-125

-150

-25

-75

-50

4S/14W-2N1, 2 PM-3 Madrid #1, 2

640-680, 480-520 (40, 28) 

West Coast Basin layer 3 

YEAR YEAR

YEAR YEAR

WATER LEVEL, IN FEET ABOVE SEA LEVEL

50

-50

-75

-100

25

-25

0

3S/14W-17G5, 6 Hawthorne-1 #3, 4 

520-540, 400-420 (30, 24)

West Coast Basin layer 3 USGS
182 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

1970 2002 1980 1990 1970 2002 1980 1990

1970 2002 1980 1970 2002 1990 1980 1990

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

50

-50

-75

-100

25

-25

0

-50

-75

-100

-125

25

-25

0

50

-50

-75

-100

25

-25

0

150

125

100

175

200

75

50

Santa Monica layer 3

50

-50

-75

-100

25

-25

0

3S/14W-17G4 Hawthorne-1 #2

710-730 (30, 24)

4S/14W-9Q1 746

241-395 (41, 25)

3S/14W-13J5 Gardena-1 #1

970-990 (31, 32)

4S/13W-28A3, 4 Wilmington-1 #1, 2

915-935, 780-800 (46, 37)

4S/13W-32F1 Wilmington-2 #1

950-970 (48, 35)

4S/14W-26A2 Lomita-1 #1

1240-1260 (45, 29)

1S/15W-31E1SMI

151-250 (12, 8)

West Coast Basin layer 3 West Coast Basin layer 4 USGS

West Coast Basin layer 4 USGS

West Coast Basin layer 4 USGS

West Coast Basin layer 4 USGS

West Coast Basin layer 4 USGS 

25

-75

-100

-125

0

-50

-25

75

-25

-50

-75

50

0

25

2S/15W-11A1 Charnock-18

103-438 (16, 17)

2S/15W-22E3 1251T 

120-185 (20, 15)

Santa Monica layer 3

Santa Monica layer 2 

YEAR YEAR

YEAR YEAR

WATER LEVEL, IN FEET ABOVE SEA LEVEL

50

-50

-75

-100

25

-25

0

4S/14W-4K PM-4 Mariner #1, 2, 3

670-710, 500-540, 340-380 (39, 24) 

West Coast Basin layer 3 
Appendix VI 183

1970 2002 1980 1990 1970 2002 1980 1990

1970 2002 1980 1970 2002 1990 1980 1990

175

75

50

25

150

100

125

50

-50

-75

-100

25

-25

0

-50

-75

-100

-125

25

-25

0

-50

-75

-100

-125

25

-25

0

200

225

250

100

75

50

175

125

150

-50

-75

-100

-125

25

-25

0

250

150

125

100

225

175

200

250

150

125

100

225

175

200

4S/11W-4K1

225-1020 (38, 61)

(nearest cell)

1S/15W-32 A5 ARC4

85-218 (11,13)

1S/14W-20M2 1380

108-438 (9,23)

3S/11W-35J3

373-678 (36, 66)

(nearest cell)

4S/11W-19R1, Q3 

266-306, 300-700 (44, 57) (nearest cell)

5S/11W-C1, C2 

548-802, 580-674 (52, 56) 

2S/11W-5L1 6M1

48-97 (16, 59)

2S/11W-6G2 SM3

44-51 (16, 58) (nearest cell) 

Hollywood Basin layer 3

Boundary wells layer 3

Orange County

Santa Monica layer 2

Boundary wells layer 3

Orange County

Boundary wells layer 3

Orange County

Boundary wells layer 3

Orange County

Boundary wells layer 1

Whittier Narrows

Boundary wells layer 1

Whittier Narrows

YEAR YEAR

YEAR YEAR

WATER LEVEL, IN FEET ABOVE SEA LEVEL

50

-50

-75

-100

25

-25

0

Santa Monica layer 3

2S/15W-4C2 SM3

210-530 (14, 13)
184 Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California

1970 2002 1980 1990

400

300

275

250

375

325

350

1S/13W-14E3

(7, 41) (nearest cell)

Boundary wells layer 1 

LA Narrows

YEAR